is it an 8 or 16v? 16v would be preferable for track days, but it depends on what kind or performance. standard engiine can be tuned up, but you can always slap some performance cams in there, have it ported and polished, loads you can do... just depends on how seriously you want to take it.
normal brakes would be okies if you had some good discs and pads, but you can always upgrade to g60 set-up or even 5 stud pattern brakes off loads of vag cars.
best thing to start with though is stripping it out. take everything out and see how it all looks, get some bits sold and get on with it.
as for weight, you'll be able to find the standard weight of a mk2 reletivly easy if you put a search i on here or google etc, but a stripped out weight...well that depends on whats been stripped, whats been saved, engine thats in it, wheels, all sorts of things make a difference. best just to strip it and see how it handles

rob