I am very new as well so hopefully some of the more senior members will chime in. What I did was buy the primary colors so you can mix them to get just about any color you need to get started. After that I started supplementing with flouro's and pearlized colors that I needed for specific projects. It can be expensive if you go blow a ton on all the colors everyone uses, so start slow with the basics and add a bottle or 2 on paydays to help get you to the next level.
Question 2: What I do is use a scotchbrite pad to knock the coating off the H20 lures and lightly scuff that paint underneath, then hit it with a coat of rattlecan primer, then airbrush to my hearts content.
I hope some of this helps, maybe some of the professionals will chime in and offer a bit more.
Billy