what types of paints to use and when

Trial and error mainly. From your own experience you will find what paints work best for airbrushing, handbrushing, dry brushing, etc. What one member here may swear by another one swears at or off. You will eventually prefer the properties of one type of paint over another for each particular type of usage.

I got it simple... My LHS sells three brands of bottle paint: Testor's Model Master Enamels & Acrylics, Testor's, & Tamiya. I use rattle-cans from Model Master and WAl-Mart too...  The main thing to remember is to use one type of paint for color-coat, the other to weather it... If you paint a model with enamel, weather it with acrylics, and vice versa...

'I use a number of craft paints though... They come in larger bottles with twice the amount and less than half the price of the above brands... You just have make comparisons with model paints, because craft paints have those cockamamee chick-names, i.e. Orchid, Mushroom, Forest Moonlight, etc...

Once you get it figured out though, you'll save a lot of money that way...

 

I use Tamiya and Model Master acrylics.  Sometimes, it's because one line doesn't have the exact color I'm looking for, while the other one does. 

Other times, though, it's because one line does a better job than the other.  For instance, if I have to handbrush something, I prefer Model Master.  The Tamiya tends to roll up if you don't wait long enough to brush a second coat.  But for airbrushing, I prefer Tamiya.  Model Master adheres to my airbrush and takes forever to clean it out.  I hate having to disassemble and soak the parts for an hour after every use.  With Tamiya, I can spray some solvent through and then a bit of distilled water and be done with the cleanup.  I can do a teardown after 4 or 5 uses.

-Fred