1) at least one in each major airline alliance. Choose the specific airlines based on what you find in question 2. Someone with detailed knowledge may be able to recommend an airline for service from SAN to Italy.
2) look at airline partners for credit cards with flexible points programs—Citi ThankYou, Chase Ultimate Rewards, and AMEX Membership Rewards and choose. Concentrate your points in one flexible points program if possible. It will make it much easier to build a useful quantity of points.
3) I know nothing.