Hi edison, already answered most of your questions in your PM but for your other questions here it is:-

2. Buy ntsc-j. The only game that i've missed out on is rock band 2 which was region locked. but that's ok because we have rock band 3 on ntsc-j now. A lot of games nowadays are region free but most of the ori games in MY are ntsc-j.

3. The xbox doesn't track serial numbers on game discs. serial numbers are used to download free dlc or rock band/guitar hero disk exports. which are one time use only. So you can buy 2nd hand or resell, just be sure to find out if the serial codes have been redeemed or not.

5. http://www.rockband.com/compatibility should answer your questions

6. No problem - my xboxlive account tracks gamer score for xbox and gfwl games. Now it should be able to track games released for windows mobile 7. Your MS points can be used to buy dlc/stuff on all platforms.