I'm not a historian by any stretch of the imagination, and I want to learn about the history of Japan. "The Making of Modern Japan" seems to be a definitive book on the subject that everyone recommends, but it only goes from the 1600s onwards, and I want to start from the beginning. It turns out that my options are pretty limited, with George Sansom's book being one of them, but that one definitely reads like it was written by someone born in the 19th century England, and an almost complete lack of any visual aids (like maps and whatnot) doesn't help either.
This leaves me with the only other option - The Cambridge History of Japan, which is extremely long and rather scary-looking for someone as unprofessional as me. So what should I do? Should I stick to Sansom's book (which gets the job done so far), switch to the Cambridge book, or are there other alternatives that I'm not aware of?
I'm a historian of Japan who works on the premodern period, and I'm thrilled you want to read good scholarship that starts "at the beginning" rather than in 1600. Fortunately you do have a lot of options. I would recommend Japan Emerging, which I use in many of my classes. Edited by Karl Friday, it contains essays by many of the top scholars in premodern Japanese history, but is written in a more accessible and less encyclopedic manner than the original CHJ. Other good overviews include Paul Varley's Japanese Culture and Souyri's The World Turned Upside Down.
My own 2016 book, Spectacular Accumulation: Material Culture, Tokugawa Ieyasu, and Samurai Sociability, looks at the cultural patronage and warfare of warlords from the late sixteenth century, focusing mostly on the founder of the Tokugawa shogunate.
Lastly I wanted to mention that a completely new version of the Cambridge History of Japan is currently underway. It will consist of three volumes--one on premodern, one on early modern, and one on modern--and should come out in 2021. I'm one of the contributors, writing an essay on the shift from medieval to early modern, focusing on the rulers Hideyoshi, Ieyasu, Hidetada, and Iemitsu. So maybe wait to read that when it comes out?
I don't know much about Japan, but I do know about Cambridge History collections, so I can tell you a bit about them generally.
While they are indeed often pretty 'long and scary', as you put it, I wouldn't necessarily let that put you off!
They usually involve collections of essays by different authors, and as far as I can see the Japan one does this too, which means they're really good for picking topics that interest you and reading about those. There will almost certainly be essays in there that you don't understand, but this is true of everyone I think. (I have a PhD in history but even on a topic I know, looking at a collection like this, are always likely to be a few essays that either don't interest me or I don't fully understand, simply because of the huge range of topics that 'history' encompasses.)
The other great thing about collections like this is usually, even if an essay itself is rather dry and complex, they often have conclusions that summarise whats in them in an easy to understand way. So I imagine you would find reading these very rewarding even if the essay itself is a bit much.
The actual content of academic history essays at that sort of level is mostly going through the evidence and establishing their argument systematically, but if you aren't actually planning to engage with their evidence in writing of your own, you don't always necessarily need to read all of this! Obviously it varies by author but in general the conclusions will contain the information you want to know, and the rest of the essay will show how they arrived at that view.
The Cambridge history collections also usually come in multiple volumes so you could always start with the first volume and go from there.
That said, I would be very surprised if there aren't plenty of 'lighter' books on the subject of Japan pre-1600 out there that might better suit what you're after, but that isn't my area at all so I couldn't comment on that. Hopefully someone else might be able to!