RedTurboAudiB6

My 1.8t a4 230 audi has very recently started doing some very strange things. My brake lights stay on while I'm driving but occasionally go out and also my revs sometimes start going up while I'm not pressing the accelerator but usually does it while I'm doing 30 to 40 mph, if i come to a stop they drop down to 1000rpm and then I can carry on fine, what's the solution!? Is it expensive!?

Hey everyone, new to the site and have a dilemma, I'm wanting to upgrade my breaks however I have no idea what size my fronts or rears are. Would very much appreciate it if someone could somehow find out what my front and break disk sizes are aswell as the break pads. Thanks in advance. My car is a 2004 audi a4 1.8T and my wheels sizes are 235/40 if it helps. Cheers!