Time to check out Garage Section at the Games Section. There are plenty of sellers here selling unmodded ones.

Modded xbox will not last you long as you need to keep updating it once new games are release.

Unmodded ones, you can update, download stuff online and never get any problems running newest and latest games. As for being online, if you do play multiplayer games, you need to subscribe to Xbox Live Gold. This is additional cost on top of the console and games.

Think about it before committing.

Save up and get a 250gb hdd. Sooner or later you'll need the HDD for demos and DLCs and to prolong the life of the optical reader (what most people say), install a portion of the game on the hdd.

As for registration, I started off with SG region. Each region has its own exclusive stuff but most of it are similar. Just be aware that MS Points are region specific.

As for Gold, I'm not sure if its region specific since there are Asia version, US version and Japan version.