Definitely a wise choice on the Bilsteins. Might be worth considering new springs though, as yours will be quite tired. See what's out there Eibach-wise.
The control arms on the Golf3 are a lot stiffer than the Golf2. If it's a daily I wouldn't, as they won't deform if you wallop a kerb, instead the shock will be dumped into your subframe et al and do nasty things, probably.
The rear bush on the control arm *might* be the same diameter as the TT genuine bush, but I would urge you to check that before buying as they're a lot more cash. It's likely to be a good upgrade if it does fit.
A rear ARB should help dial out some understeer, but I'd drive the tits off it before deciding to go down that route.
As for the Genuine parts, unless you can get a really good deal on them, see what price top quality bits from GSF or ECP are - for what you're doing they're likely as not to be same manufacturer with their logo on instead of the VW logo.
Lastly go to a good alignment place and get factory settings on the front, but dial in either -0.5 or -1 camber on the front wheels. This may give you enough improved turn in and front grip to negate the need for a rear ARB.