Green card holder - Enlist

Hello everyone!

I’m planning to enlist in USAF soonish but I'll be only a Green Card Holder by then.

My first question is: can I join as an E3 or E4? I have a bachelors degree in Finances. A recruiter told me, that I could join as an E4 (Army, but I prefer AF)...

My second question is: do the following jobs require a U.S. Citizenship? Contracting, Public Affairs, Finances, Cyber Security (ik, that CS does... please read question 3 as well...)

My third question: I read, that some GC Holder can get their Citizenship during BMT. Is there any other condition with getting the Citizenship during BMT? And can I get a job like Cyber that way?

My last job option: Would anyone recommend Nursing? If so, can I go to Med School while being enlisted and try to apply for the Officer path after graduating? That would take forever, right?... 6-8 years Med School (at least in Germany, not sure about the ones in the USA)

TIA! :)