You don't want to mix paints from various manufacturers, but you can apply multiple coats of paint, each of which is from a different manufacturer.  You want to wait till the bottom coat is fully cured till you paint another coat on top of it.  The general rule is to apply lacquers first, enamels next, and then acrylics on top.  If you switch the order around you may find the paint you are applying is dissolving the coat below it.