Hey! I just joined the site, but I have been airbrushing for quite a few years, and taught it for a few at the local college. I'm familiar with Iwatas, Createx, and how the two work together. Hope I can answer some of your questions to your satisfaction.
1) When applying candy, it has to be mixed with the transparent reducer! Use the candies over anything, but metallics and 'hot' colours look the best. White is always a good base for candies too. Because painting candies too heavy will always tend to black, painting them in light passes over light colours is always the best show, but they can be used to intensify darker colours.
2) I use the aluminum paints as a base mainly, but have mixed a drop or two into colours to add sparkle. The aluminums are literally ground aluminum in a clear medium, so they don't tend to tint your colour when you add them.
3) I don't know of any good recipes, I just look at a picture of the colour/fade/transition I want to paint then paint what you see. A colour wheel would be a good cheap investment. You'll learn what colours look good together, and how to mix them, either in the brish or laying the paint.
I'm just finishing up my first few baits and will be basing/sealing them tomorrow, I'll take pictures of my painting progress for you if you want. You can check out some of my work at www.freewebs.com/criticalair/
Critical Air