You can use just about any kind of paint on Papier mâché. The most commonly used is acrylic but water based paints work well too. You can make the paint as runny as you like, to get rainbow effects and smudging. Just make sure that you don't use a water based varnish on top of poster paint!

As for a turntable, this is my most valued piece of kit for my work. I use it while I'm actually making something, as well as painting. It enables you to observe the object from all sides without constantly picking it up and risking damaging it.

I know someone who only uses spray car paints on their work and it gives a very professional looking finish. Just be careful of the fumes, especially inside a box. Make sure the windows are open for ventilation, or better still do it outside.

I use latex house paints as my base (typically black) and my drybrush coat (some shade of oops white) -- which lets me highlight the slightly stone-like texture of the surface.  Then I use craft store acrylics that I dapple or sponge on to create some more color variations. 

The latex gives a bit of water resistance.  (Note resistance, not waterproofing).  And is cheap for a solid basecoat. 

In lieu of spray paint or airbrush, for a faded color (or any other color change technique) I do a wet on wet technique where I mix in a bit more of the other color (or white if it's a fade) as I paint up the piece.  For most acrylics you'll need to add an extender, however, that will prevent it from drying too quickly ... 

It takes some practice, but for me, still way cheaper / easier than purchasing / learning to air brush.  : )

-- b