You should check out the 1/12th scale thread. There are a few people there who have setup old saddle pack style chassis to run the 1s LiPo on one side of the chassis with the electronics on the other.
As for what to get...well that depends. Are you taking it to the local track or just going to blast around in a parking lot? If racing it you'll need to find out what class they are running. I think most of the US is running a 17.5 blinky class for 1/12th if they have a 1/12th class. Ours is 13.5 blinky. Blinky refers to the profile in the ESC that has no additional timing for the motor. There is a specific light(s) that blink so that tech inspectors at a race can visually see the car is running a legal profile. If your just playing around in a parking lot you'll probably find 17.5 too slow for your liking and I would suggest a 13.5 motor...beyond that it starts to border on uncontrollable at least for me. For an ESC you'll either need to get one with a voltage booster built in or run a separate voltage booster or battery pack to power the receiver. You'll need a new charger as well as your old one will not charge the new batteries.
Good info thread:
12th Scale Racing is Alive and Well in So Cal