This is the first year in the last seven we're not doing a search. I've been involved in a few of these, and never do they last just one semester. I can tell you that, the way we do them, they're all difficult in different ways; our US search had over 500 applicants and required difficult winnowing of very dissimilarly strong candidates, while our Middle East search had about 40 applicants and the ones we wanted kept getting scooped up by even bigger and better-funded institutions before we could make the hire. Part of the difficulty is that we really do read every application and all the supporting materials before deciding--we don't have any "magic automatic disqualifiers" beyond those in the job listing itself, like area of specialization, Ph.D., and so forth. But one trend that has been constant since 2008 is the move towards electronic tender of applications (whether Interfolio or emailed PDFs, with a snail option always provided for) and Skype for interviews instead of sending committees off to AHA. In our experience, it benefits us to go through our process earlier than AHA convenes anyway.
In the fall, we collect applications and get to our short-list. We interview in December. We invite candidates in January. We then make offers in late January, and getting a contract signed and approved requires negotiations that can last into April if we've had candidates drop out for whatever reason. The collection of applications and their evaluation is only part of the whole, and it's arguably not always the most difficult portion.
Adjuncts we hire on an ad hoc basis, depending on needs, from an approved pool; visiting positions fall under that category. That's Dept Steering Committee and undergrad director stuff, not for the whole Department.
Unless you are exclusively interested in answers from historians, this question might do better in /r/AskAcademia.
In addition to /u/estherke's recommendation, you might also wish to post this question in today's Academic/Professional thread -- it tends to attract more of the sort of readers who might be able to give you the answers you seek.
I am traveling and on my iPad but by Saturday I can answer this more extensively. We did a hire last year and will do another one this year. I also have done professional development workshops on hiring tips. Of course your mileage will vary depending on the institution you are applying to and the type of position -- a research institution will have differing criteria for screening than a two year college will and different from that of say a small private college where tenure still considers research but teaching may have greater weight than publication history. The culture of the department and the Dean or VPI can also have strong influences.
On Saturday I'll come back and do on overview of your questions, but if you have any other specific questions I shall do my best to answer them. In some cases due to confidentiality I may be required to speak in generalities, however.
As a two year college our hiring of Adjuncts is much more relaxed and doesn't involve a committee -- in general I hire the Americanists and a colleague of mine is in charge on hiring the Europeanists.