Ideally you need to put solvent paint down first and back with water based. However as long as you have a nice heat gun and heat it to the point just before the paint blisters to make sure it's thoroughly dry you can use it in pretty much any order you want
Createx is essentially what I think everyone uses on here ( even me
) and despite my hatred of it they do make some quite gorgeous colours
and it easy to clean up ( use wind screen wash, cleans it all up fine and doesn't effect any of the rubber seals in your airbrush ( if it has them ). Jon sells the Createx stuff but it's the same as available from else where, essentially though Jon is everyone's one stop shop and is no cheaper or expensive than anyone else, also his solvent based paint is great, shame he won't develop it for the hardcore fume loving idiot's like myself
If you like Solvent based stuff I think Custom Colour did do a solvent range but they don't have the spectrum of colours available through Createx.