1 if you want to just give 4 yrs and get out, you'd most likely be stationed in one spot and do 4.
2 i was told it's really 99% up to your spouse to find a job. it really depends on the location and the career field. check out ft irwin and bethesda, md, for example, to see the difference.
3 it depends on your duty station, but if you want just give 4 yrs and then get out, you probably won't learn much--you'll have a lot of catching up to do. search threads. there are plenty of discussions on sdn about this.
4 no. there are plenty of officers who were never deployed. the formula is much more complicated than that: you could be assigned to be a brig dentist or you could volunteer. yes, there are many volunteers for many reasons.
5 i haven't deployed, so i don't know but people told me once inside fob (forward op base), you are pretty safe. remember, IEDs go off when you are moving from pt a to pt b. i haven't heard a single military dentist died or critically injured
6 combat deployment. it could be location specific, but i wouldn't worry about that for now. it probably won't be applicable to you, anyway.
7 closed to zero.
8 i don't think so, but the program has been getting more competitive every year. but with good stats, you should not have a problem. i don't know exactly how many are left (any hard numbers being tossed around sdn might not be accurate, fyi)