Munkeh - As long as the X360's power source is plugged in (ie, electicity going to the 360), yes, you can charge the 360's wireless controllers via the Play & Charge kit.
And yes, I'd just get a P&C kit for each color controller. To be frugal, you *might* be able to find just the battery packs, and/or just the power cord. Reason I say this is I've seen kits for $15 USD that include the charge cord and 2 battery packs (as opposed to paying $30+ for 2 cords + 2 packs).
Chrizum - For buying content on Gold, you have only 2 ways to pay for it.
#1. Submit Credit Card information to Microsoft via XBL for purchasing Gold subscriptions, or Microsoft Points. You can have multiple CCs, and info as you wish.
#2. Buy in a "store". I say "store", because you can buy them at any retail electronics store, and Ebay. Again, buying offline can be GREAT because some stores have 2 for 1 deals every so often. So all of a sudden, that $10 copy of Ikaruga becomes $5..PSNetwork doesn't have the cards, therefore doesn't have the steals of the century (I know of a few NeoGAF members that have bought $100+ of XBLA games and content for half price just buy being smart about the offline deals for the MSP Cards).
Back from the dead, I'm afraid.
