The brake light should light up on the dash when the pads are wearing out. They have a wire on them that grounds to the disc's when the pads get thin.
The thermostat should hopefully not give you any problems. If it does it will generally do one of two things, either stick open - engine will run cold - take a long time to heat up, or stick closed - the engine will overheat - not good.
Cheers
Rossco
1996 E36 320i
