https://www.benning.army.mil/7...recruiting/index.htm that website has all of the info you could possibly need on ranger recruiting. Im pretty sure that you cant re enlist for rip, and ft. lewis, and from what my friends have said after rip they send you wherever you are needed.
Ranger is a school/ASI you can reenlist for it as long as other prequals are met. 6 months before ETS is when CC's realize how serious you are about your goals, and may be more inclined to assist. A CC can correct me if I am wrong on this.