Questions about historiography and the historical method are absolutely welcome (and even encouraged) on this sub-reddit; we actually have two weekly features (Monday Methods and Thursday Theory) dedicated to exploring historiographical discussions and debates. Contrary to being stupid, the questions you pose are actually ones which have been richly discussed by historians of every stature for decades.

1. To what degree can we talk about consensus in the field?

It is important to understand that there is a distinction to be made between a historical fact and absolute truth; a distinction between history and the past. Contrary to how the word tends to be used, history is not the same as the past. The past is what actually happened, the physical reality that once occurred and is now lost. History is the understanding we have today about what happened in the past (and who it involved, and how it happened, and why it happened); it is a narrative we create in a bid to try and reconstruct the past. How far history can succeed in authentically recapturing the physical reality of the past is very strongly contested, but I think it's safe to say most historians and students of history would tell you that complete reconstruction is impossible, for a whole variety of reasons.

Historical consensus emerges from the process of exploring the various possible interpretations of the historical record and considering which seem to be the best supported. The extent to which it is possible to achieve a strong consensus varies depending on what it is you're talking about; certainly, there are orthodoxies that have been so well constructed that it is highly unlikely they will ever be meaningfully challenged. Historians are nonetheless constantly engaged in a process of evaluating and re-evaluating established orthodoxies. Finding new source material and critically challenging existing interpretations of old source material are both an important part of the process by which historical consensus is formed.

Even when historians discover a treasure trove of new source material that's never been used before, if that source material contradicts existing orthodoxies, they have to demonstrate why and how it does that; that usually means using the new material to reframe analysis of older material on which orthodox views are based. The essential thing is that all interpretations must be drawn out from the historical record - and a critical engagement with it, at that. Holocaust denial, for instance, is only possible if you are highly selective in the sources you engage with and very weak in your methodological approach. Historians can recognise differing, legitimate interpretations of the record whilst holding one in higher regard than another.

I had a little bit of a discussion on the idea of what constitutes 'historical reality' here, which you might find interesting.

2. What are best ways to both avoid one's and recognize other's bias? [...] Thus even if someone tries to be objective, things like religion, upbringing and peers' opinion will always, even if subconsciously, affect the interpretation.

This is one of the fundamental (and essentially unresolved) problems in historical theory. Entire volumes have been dedicated to this topic. To some extent, you can say that today, we are all post-modernists. You would be hard pressed to find a serious historian who believes in objective truth in everything, or that they are entirely free of bias. In some cases, bias is arguably desirable and good - I would be profoundly unsettled by any scholar who claimed to have no moral stance on slavery, and a lot of fantastic research has come from historians who have pursued their own interests. Many students of history are motivated to chase a specific aspect of historical studies based on their own experiences or identity; I would by lying if I denied my interest in labour history doesn't have a lot to do with my own urban working class upbringing, for example.

In methodological terms, historians generally try to avoid bias in a two-fold fashion. First, we make our arguments from the historical record; from the primary source material. Whilst you go into historical research with an initial idea or feeling about what direction your writing will probably go in (that's inevitable), historians construct their arguments based on their honest, critical interpretation of source material. In essence, historical research is a kind of problem solving: you give yourself an unsolved question to answer, and you must build your answer on the basis of the evidence you have to hand.

That sometimes means you end up coming to conclusions that you do not necessarily like in a moral or political sense of the word. When you encounter source material that challenges your current thinking, you cannot simply ignore it. Instead you have two options: either you must demonstrate why that source does not undermine your argument (based on your analysis of other source material or the work of other scholars), or you must reconsider your current thinking in light of the new material. Hiding from or avoiding the challenge is simply not an option if you wish to write good history. In that sense then, historians try to be earnestly self-critical as well as critical of one another.

The other key thing good historical research tries to do is understand the past in its proper context. The extent to which we can do that is similarly debated, but we certainly try to. In essence you could say that historians try to understand the people of the past without necessarily sympathising with them. I would say I can understand quite well, for instance, the kind of complex morality a southern slave holder would have used to rationalise and justify slavery as a moral good; I can (try to) articulate that morality in a narrative without casting the slave holder as either the villain or the hero of the story, but rather as just another actor of significance worth understanding. I try to understand him somewhat as he would have understood himself, albeit in a more critical light, as much as I possibly can with the evidence I have to hand. In myself though, I am obviously much more morally sympathetic to his slaves than I could ever be to him.

Bias can never be escaped in history, but it can be profoundly mitigated and its manifestations are - in good historical work - subtle and hopefully recognised.

3. How does peer review process work for historians?

I'm going to leave this for someone else to tackle who has much more experience with this topic because I am, alas, in my relative academic infancy, and so have not yet been driven into insanity by my career choice only limited experience in getting work published.

I'll tackle the basics of question 3, since u/sowser did such a great job on the first two.

So peer review works in two basic ways, which I'll call pre- and post-publication.

Before a piece is published, whether as a book or a journal article, the piece is sent off to an editor/publisher. That person reads the work (or a proposal if we're talking about a book) and decides whether its worthy of publishing. Once the work is "finished" by the author, the author sends it to the editor/publisher, who then asks people competent in the field to offer anonymous reviews (the general number is three, but this can vary). Only the publisher knows who these reviewers are, the original author has no idea, although if the field is small enough, the author might be able to guess. The anonymity is important because it allows the reviewers to offer an honest opinion without potentially burning bridges or relationships. The reviewers then offer critiques which the editor/publisher then returns to the original author with a note saying to fix and resubmit. Very, very, very rarely, do the anonymous reviewers, as a group, have nothing to critique. One might think the work is great, another might disagree with substantial portions, and the third might have only minor qualms. All three might have qualms with a specific section or different sections. One might suggest additional investigation of a not yet included topic as a form of comparison, and so on and so forth. The extent to which the author has to abide by these requests is up to the author and the editor/publisher jointly. If the publisher disagrees with the reviewers (or the author is able to convince the publisher that the reviewer is incorrect), then those suggestions for edits can be scrapped. Whether this happens or not is a case by case basis. Once the publisher is happy with the work, then they go forward and publish (there are other steps like copy editing, indexing, and such, but those aren't really involved with peer review, so I'll not bother discussing those).

The post-publication part deals with the response within the field. If the publication is a book, then the first point is academic reviews. These generally come in the form of journal reviews in which scholars in the field are asked to review new books by journal editors. Every journal (well the vast majority) contain a section on new works in each edition that are made up of reviews by scholars of said new works. The other main way that peer review works (and this counts for both journal articles and books) is through the academic conversation process. One of the main things that separates academic history from hobbyist history is that academic works are in conversation with each other. They are constantly referencing other works, back and forth. If person X writes a book that person Y just completely disagrees with, and both are experts in the field, then it's likely that person Y will go back to the archive (or other source material) and write a book in response. The field that this is most easily visible to the laymen is in the historiography of the French Revolution. There have been several periods of historical consensus and orthodoxy over the last hundred years. Tocqueville's orthodoxy was overthrown by Marxists (Soboul or Lefebvre - the rising bourgeoisie overthrowing the feudal aristocracy), whose orthodoxy was overthrown by revisionists (Cobban or Furet - it's all about politics, man, not economics), whose orthodoxy was overthrown by post-revisionists (DuBois or Desan - its about much more than white men in the metropole). All of these works by scholars of the French Revolution are in conversation with the works that preceded them, mainly to argue how the folks before them got it wrong. This is a never-ending process, as u/sowser pointed out, because even if these is a consensus, someone will, invariably come along and challenge that consensus with new sources, new methods, new frameworks, etc. In that sense, academic history is nothing more than one giant argument with peer review being the primary medium through which that argument takes place.

EDIT: I should mention that in the anonymous review process, it is possible that a work gets rejected outright. It's rare, generally because editors/publishers have a pretty good understanding of the field, but they do make mistakes that only experts might catch. But by and large, at academic journals and academic presses, the publishers specialize in specific topics and so have a pretty good understanding of the state of the field in that topic. How it works for giant journals, like the American Historical Review, I cannot say. Getting published in the AHR is something that historians can go an entire career without ever experiencing.