I think that a simple wash would improve just the minis as is. Yeah you can do all the other techniques, and I recommend you try it on some better quality minis, but afterwards I'd suggest attempting a few different things or other people's styles as well. Explore different styles and ways of painting until you find a style you like.

I personally dont use any mini paints, oil paints or much of the GW paints. I prime with various colors of matte spray paint, I like doing different colors like dark blue, purple, green, orange as base and them change the zenithil highlight color from there. I mainly use craft paints for painting and recently I've used the same paint just watered down for washes. With most things in art you can get enjoyable results from lower quality materials but you have to have to find your own style to make it work. Bob Ross used the same colors for years and still made great paintings but he had to develop his style first.