I can only answer a few of these (since I'm not in CAS)...
2. Yes, all freshmen live on North. But there is a medley of housing, including program houses w/upperclassmen, so you'll probably end up somewhere you love (given that you're honest on your housing app). Housing is NOT guaranteed all 4 years- only freshmen and sophomore year. Sophomores usually live on West Campus (a few new 'houses' down there) and upperclassmen live either in program houses, co-ops, West Campus/Collegetown dorms, fraternity/sorority houses, or off-campus houses/apartments (in Collegetown, near North/West, downtown). I'm finding that most of my friends are living on West next year (soph. year), some in C-town dorms, and the rest in sororities or off-campus housing.
4. A prelim is like a midterm test- cumulative up to that point, but usually it's twice a semester, thus nullifying the 'midterm' name. Each class has different number, types, intensity of prelims, so you'd really have to look into the classes you'd be taking (ie. Calc I has 3 prelims; a lot of history classes just have many papers).
6. Yes. Your First Year Writing Seminar will be open to all students, and although it may be concentrated (ie. one of the English ones like Intro to Poetry might be more CAS/English majors), it will probably be diverse. My FWS had Hotelies, Arts and Sci kids, ILRies, and Aggies, and it was in the AAP school (go figure). Your dorm/room/friends will most likely be in other majors/schools, without a doubt. A lot of CAS classes are also full of people from other schools, too, so you won't just be seeing the same people (unless you're in a small school like mine and you get to know your class very well).
7) Most people will walk, and at most it'll be 20 minutes (it depends how fast you walk, too). Sometimes you'll take a bus if you catch one/plan for it, especially when it's cold, but it's really not that bad. It is (in my opinion) more hilly than other schools I've visited, but then again, I grew up near farms and in a valley, so what do I know?
8. Ithaca in the summer, from what I know (I came here twice in the summer) was fairly hot but not overly humid. Perhaps someone who's come for the HS Summer Program can answer that better.
Hope this helps!