The Espruino MDBT42 breakouts is a good shout, but my Pixl.js turned up this morning. I opted for it specifically for the Bluetooth integration, but couldn't say no to the screen as well. Longer term I'm hoping to add an accelerometer and Gyro to see if I can get it to be completely autonomous.
I would definitely be looking to on-board the power supply for the espruino and the motor, quite happy for these to be separate. The challenge I'm currently investigating is the power draw of the motors and the battery supply that would be needed to power it. It appears that traditionally the motors run on 12 volts for 18,000 rpm (they do require a gearbox). The flip side of this of course is going to be weight. I know that the newer cars have magnets to improve down-force, I'm hoping that the weight of the batteries may somehow be mitigated by removing this magnet.