Certainly for raiders I would paint in assemblies. Don't glue it together, instead paint all metal areas, then black and yellow, and after these are done (or at least basecoatwd) then glue em together. Will save a lot of time and hassle (I know this from bitter experience).
Prime your planned Yellow assemblies in white (painting yellow is a pain, but white is the best primer colour to get better coverage) and the rest in black. Alternatively army painter do a good range of coloured primers that will save you a lot of time, and are pretty good.
For the infantry I would at least leave the guns off so you can reach the chest areas etc, and then attach them once both are painted. Same goes for the riders on the jet bikes .
Hope some of that helps a little