Oh MY! Babbitt bearings! I haven't seen those in YEARS!! Where did you get this thing? Those are some small axle shafts! What kind of scope did it hold, originally?
Sand blasting is great, but, bead blasting is better. Sand can actually get stuck in the metal and can ruin a paint job when it breaks lose. Bead blasting material has less of a tendency to stick to the metal and leaves a better finish. You will still need to do some sanding to get the finish smooth, though.
As soon as you get the metal cleaned up, immediately after blasting it and sanding it. You can lay down a primer coat to protect it. However, that will only be good for short term protection since primer can attract moisture and eventually the rust will begin developing again.
I do not know if powder coat will work with primer paint. I kind of doubt it. For something like this, especially where lead and Babbitt material are involved, I'd stick with a good enamel paint and forget about the powder coating.
By the way, I still have some old lead counterweights that I cast on my mothers kitchen stove. They were never painted and work just fine. I never even painted them. LOL
6" f/15 Jaegers refractor on GOTO GEM
5.1" f/8 Burgess on CG-5 w/ iOptron GOTONOVA
102mm f/7 refractor on iOptron Mini Tower
1975 Celestron Orange Tube C8 on Equatorial Mini Tower
1978 RV-6 on iOptron Mini Tower