When joining as a prior service, will I be able to pick what job I want, become needs of the Army, or go back to my old MOS?

A big potential influence on available MOSs is your GT score on the ASVAB.

I know that re-joining works different than initial enlistment OR standard re-enlistment. I do not know the rules, so take this with a grain of salt, but....

You are not in the Army right now, and you have no requirement to be. If you do not like your options, you have the ability to walk away.

I recommend talking to a local recruiter, and see what (s)he has to say. If you don't like those answers, try a recruiter at a nearby recruiting station.

I will also toss this out to SFC (Join to see) . He appears to be an all-knowing God when it comes to retention (or at least all-referencing), and re-entering is not his *specific* field of expertise. But he is still pretty doggone knowledgeable with that avenue, and can probably get you headed in the right direction better than most of us on RP can.

You have more leverage now than a PVT E-9. Use it wisely, Good Luck