Wow. Long novel. Probably wouldn't read again. I'll just answer what I can / what I know and leave everything else up to other people to answer for you.
Are the DO school admission stats (average cumulative and science GPAs) reported online using the aacomas GPA calculation method (ie with grade replacement, only including bio/chem/physics in science, etc.)? Or are these stats not including grade replacement and other aacomas gpa rules? My GPA is much lower than what I wrote above without grade replacement, so I want to make sure I'm actually close to the average range at some DO schools.
Here is a list of stats someone on sdn posted:
http://forums.studentdoctor.net/threads/stats-for-osteopathic-medical-schools.598056
As far as I know, any stats that you see reported online are taken from the schools directly. Some publish their numbers online, some don't. I don't believe AACOMAS publishes the numbers for each individual school. I could be mistaken on this though. Also, I would assume that the GPAs given online for each school include grade replacements to make them look a little nicer.
I will still be taking a few courses this coming winter and spring quarters for my postbacc, but I realized that the spring quarter grades will not be finalized until June 15th at the latest. If I'm finished with all my other application materials and my mcat score is back by then (which it should be since I'm hoping to take the 5/14 mcat), is mid to late June considered "late" to apply? I know it technically isn't, but considering my not-so-hot gpa, I just don't want to be at a disadvantage by applying in late June since I know people can start submitting aacomas apps as early as mid May. I'm thinking of sending my undergrad transcript in May so it starts getting there and just send my postbacc transcript in mid June once my grades are in. I can submit my app online in late May probably. But I know I won't be verified til mid July probably and I hope that's not too late??
Relax. Mid to late June is not late at all. I would say applying anytime during the Summer months would be considered pretty early for AACOMAS regardless of your GPA, maybe not so much for AMCAS. Your GPA isn't terrible for applying DO.
I am self-studying for the MCAT from now until May (may 14 test date) with all princeton review materials. I'm trying to come up with a good self-studying schedule but am struggling a little. Most schedules on sdn incorporate lots of other test prep resources as well but I just want to focus on the PR resources I have right now. Does anyone have any tips on a self-study schedule using just PR materials for now? Also, how many practice tests should I seek out overall to get "enough" practice? Is it enough for me to just use PR books to prepare and then take as many practice tests I can find/afford, or should I definitely try to also use other test prep company resources (kaplan, EK, etc)?
Other people will probably give you better advice on this than me, but I would recommend doing what you feel most comfortable with doing. Everybody has a different schedule/plan for doing well on the MCAT. Personally though, I would say that sticking to just the Princeton Review material should be enough. If you've got some money to spare, I'd recommend also getting ExamKracker books and using those after you've already gone through TPR. Practice is definitely the way to go though. Learning the content material will only get you so far. The MCAT is a critical thinking exam. The absolute biggest mistake that students make time after time is pouring the majority of their study time into reading content books. Definitely go through the TPR online practice material if you have access to them. I don't know if I can recommend their practice exams though. They tested pretty heavily on content and the real exam is nothing like that
Do I definitely NEED a humanities letter of rec for any DO schools (or is just recommended by some)? Since I've taken mostly science classes in the last couple years, I don't really have anyone I can ask for a humanities-type LOR.
Not to my knowledge, though I haven't looked at the requirements for every school. I applied to about 10-15 schools and I didn't have a letter from a humanities professor. I believe most of my classmates don't have one either. Between all of us we've gotten into quite a few DO schools. Take this part with a grain of salt though because I'm really not sure.
Because of medical reasons related to depression, I graduated a semester late because I didn't finish all my coursework. Would anyone in med school admissions ask me why I graduated a semester late? What should I say?
Lots of people graduate a semester late, even a year late. They probably won't ask you anything about it unless you have some sort of major red flag on your application.
I saw that most DO schools require “Six semester hours of English composition and literature." Would a writing course and a literature class suffice?
At my university, we were required to have 6 hours of English classes. Both classes I took were taken under the English department, one of which was a writing and literature course.