a) yes your enlisted time gets counted towards retirement and if greater than 4yrs it will put you at an O-1e when you commission...puts a lil extra jingle in your pockets than just straight O-1
b) There is a website that states everything you would need to purchase for BOLC
http://www.cs.amedd.army.mil/obc/ uniform requirment is located in the BOLC information packet link. this will be an out of pocket expense and you will drop like $1000-1500 and the army will pacify you by reimbursing a one time $600 payment...but something is better than nothing.
c)nursing school tips...study, dont fall behind, read, when you want to quit or throw spit balls at your instructors back remember the bigger picture...it's just 4 semesters of upper division you can do it.
d) not sure about rotc you may be a touch to old...i believe the cut off is 26 but may want to find an amedd recruiter and ask