I am a prior service Marine joining the Army (15T) as a Sgt. Is there a minimum/maximum rank you must be to become a crew chief?

There is no minimum or really max for being a crew chief. Typically flight companies choose the most competent and motivated soldiers from the D Co to move over. Once in a flight company you will stay until you are at least a SSG. At that point you may move to the QC shop or maintenance PLT in D Co to lead maintenance until you ate selected for SFC. Then it is quite possible you are back to the Flight Company to be a PLT SGT and continue your flight career. Beyond that it is 1SG time, however I have even had 1SGs who still crewed the aircraft and we're on flight status. I have even CSMs crew as door gunners on deployments to assist the flight companies and give the crew chiefs much needed time off. Learn the aircraft and stay motivated. AIT you "should" be in a prior service company and treated as such. You will go to class with the PVTs but "should" be treated like an NCO in all other aspects. I will verify this with former crew chiefs who are now at Ft. Eustis teaching the course. Good luck and if you have any other questions please ask.

No minimums to be a crew chief, and if you stay in long enough to make SFC then you can still fly as a PLT SGT. I am retiring this month and was still flying up until my unit deployed and took all their toys with them. Welcome to Army Aviation and Semper Fly!

Also, will I be treated like the average boot asshole in AIT even though I have 5 years of prior Marine Corps service? Not looking forward to that, if so... lol