Due to the Retention Control points I may not be able to re-class and be promoted in time. Would my contract length grant me more time?

In aviation promotions are more likely in an airframe MOS (R, T, U) than in a back shops MOS. In the Guard though, promotions are often very slow just because slots are so limited regardless of MOS.

Are you talking about going Guard or Active? Because RCPs aren't even a thing in the Guard that I'm aware of. As long as you get your NCOES schools and courses complete, it's just a matter of when the slots open up. Also in the Guard, you don't get "selected" for B/A/S/MLC, when you're eligible because you have your TiS/TiG and SSDs completed, they'll go into ATRRS and enter you for a school date.

Option 3: prime power generator. Promotion potential is endless, because everybody LEAVES! The recruiters are at the gates with their business cards with this MOS.

This says you're in the Guard, so retention control points don't apply. If you are going active:
1. You might not be eligible because of RCP but if the MEPS allows you in, you'll get more than enough time till your ETS date to complete school and promote - unless you're a slacker, in which case, promotion wasn't important enough to you and you'll separate. Thank you for your service.
2. Look at the HRC Enlisted promotions web site and see the historical promotion points for SGT & SSG to decide if it's hard or not. I was a medic and picked up SGT & SSG at 695 and 777. Everything is harder than Infantry in terms of promoting in the Army, but it's very doable.
3. Was there a 3?
4. You'll be given plenty of time to promote. If you suck at life and fail to keep up with your peers you'll receive a reenlistment prohibition code of 9G that prevents you from reenlisting until you promote. You will ETS and be eligible for full separation pay if you commit to three years reserve duty.

My tip is, if HRC allows you to take these low density MOSs, accept that promotions suck and you'll need college, PT, and correspondence courses to pin. These MOS's seem awesome from the outside but if you aren't competitive they will chew you up and spit you out as a terminal E4 or E5. People leave these MOS's to get promoted. So when you enroll, start working on the work to pin SFC. The qualifications that would get you promoted to E7 in Infantry will barely make points for E5 in other jobs.
Good luck on your next job.