How may sets of font family including styles i.e. ital, bold, roman, etc. in each project and do you mix serif and sans serif in a given layout?

The sets of the font family varies according to the typeface and how it was designed. Ofcourse you have to be using a design based software while doing the layout since the MS office might have a forced style that was not intentionally designed for the font.If you are using a sans serif font for the body text then you can use serif fonts for the title texts, however I would stick to one build with different weights of the same typeface. This is just a recomendation ofcourse; there is no specific rule against doing other wise but the fact that you might need to limit the number of different typefaces you use to a max of three.