I read serifed fonts may be easier to pick up so I'm wondering which of the following fonts would be a better choice for my needs:
- Georgia
- Cambria
- Palatino Linotype
You can't go wrong with Palatino. Well, you can, but you won't. Constantia, one of the new Windows C series, is similar in style but a shade less flashy.
Gentium is fine, but a bit condensed (like Times), and I think the larger x-height makes it look less formal.
Eventually, what's the suggested leading (line spacing) for business letters?
Depends on the font. With Palatino LT or Constantia, for instance, you can safely stick to 12 on 12, i.e. no additional spacing. Gentium needs an extra point or even two, I think, so as not to look too crowded. [Edit: Gentium Plus, on the other hand, probably needs one point tightening, since there's so much room for all the myriad accents.]
Should I use kerning?
Always.