Yes i had a Mk2 VW Polo Coupe S and the handbrake light was staying on, a temporary fix is to dis connect the brake fluid level sensor which is located on the resisvour. just top up the fluid and it should go out.
For the petrol situation, can u smell petrol, if so there could be a leak, and also if the thermostat is not working properly, it could be telling the engine that it is cold and using more fuel. Hope i could help, Gary