RE: Warhammer Army Planning, going from 3000pts to 5000pts and beyond.

Another option is to get all the unbuilt/unpainted plastic rank & file, get them assembled and give them a hasty paintjob with an aerosol basecoat followed by what we call "dip & flick". A quick dunk in a dipping wash, flick off the excess and then when it's dry spend 30 seconds on each figure picking out a key item or two (guns, shoulder pads, highlights or whatever).

Give the bases a quick wash with a different colour and you can put together a huge number of ordinary infantry really fast, then add detail at a later stage.