1. How many online games can be played with the silver subscribtion.
2. How often to you have to pay for XBL gold, is it monthly?
1. none. actually, you can play Phantasy Star Online with a silver account, but you still need to pay sega a fee for playing. i think that's how most MMO's are going to work on the 360.
2. xbox sells 3 different subscription cards: 1 month, 3 month, or 12 month cards. you can either buy them at any store or through xbox live with a credit card.
Also, I think if you buy the 12 month card (when I bought it, it was under $50), you get an extra month free!