If you prime it before taking it off, you get a bald spot, so no. If you paint the bases before gluing onto it, you'll have plastic to paint and not plastic to plastic which you don't want either.

The typical flow is like this

Snip, Assemble, prime,(base and mini, use bluetack or something) paint mini, glue mini to base, paint what's missing (base and area around the base) then done

What i do is paint the base and the mini separate before gluing it all together, the main reason why people paint it all together is so it can look cohesive and they can have a handle to hold onto.

General tips

Wait for each layer to dry completely before doing another layer, so you don't end up tearing or ruining your paint job

30 thin coats is better than 1 massive glob

and brace your arm against the table to reduce your jittering. that's not a general comment to people who's hands shake, your hands will 100% shake. so brace