That's a 170 isn't it? I had a 170 A3 TDI and if you only do round town driving the DPF fills up quickly and then it starts screaming at you to empty it, which involves driving at 50mph in third gear for like 20 mins. And you have to do this otherwise it will fill up so much it can never be emptied and can be a fire hazard. This was the whole reason we now have a 140 A3 TDI and not a 170.
The VW list states single part nos except for the slide rails there is a choice depending on engine no. The Audi list has other variable part nos as you can see. You said you had the Audi engine didnt you?
if you're gonna be chopping and changing then coilovers would be better, the ride is fairly subjective though, and each variant would have its own firmness, some will be much harder than others whether its fixed or coilovers
Later models have a better abs system that used the rear rings to make sure they don't lock up, earlier systems used the bias valve to give more rear braking when there was more weight over the axle
if you turn the ignition on they re centre dont they? then you could put them back on at zero. You could test the speed with GPS, the revs with vagcom, the fuel gauge you could take the fuel pump cover off and move the sender through its range of motion (it also rests at zero when the ignition is off) and the temp you know that when its good and hot it will stay solid on 90 so could use a bit of trial and error with that (also rests at zero when ignition off)
Of a mk4 R32 and a mk5 GTI I'd get the GTI every day, and put a remap in it and while not 4wd it'll be fair quick, I couldn't walk out of my house every day to a mk4 I did it and it depressed me so I sold it
Be sure to thoroughly flush the sh!t out of the block with the water pump out, rad, matrix, oil cooler, if you are doing crack pipe then do thermo housing and thermostat aswell and with all new deals too
Here's how I did mine, with no more than a jack and the front wheels driven onto blocks http://www.vr6oc.com/e107_plugins/forum/forum_viewtopic.php?344740.90#post_474111