never had a V6 but i can comment on the 2.3 20v Quattro Coupe.
suspension bushes go on a regular basis so make sure you have a good look at all the bushes in the lower arms (front and back). not sure about the power steering pump thing, i've had 3 coupes or quattros and not had trouble with any of them.
the multi function temp sender goes regularly so check it comes up to temp on the gauge in a timely manner. brakes are pretty cheap to replace compared to other cars i've owned but check the handbrake works properly, they can be pretty dire at the best of times, a pair of callipers is the best fix.
check in the wells in the boot for water, the seals go on the rear lights allowing the boot to fill up. also if it's had a new windscreen at any point you can usually tell because the front carpets will be soaked, they never seem to get the seals right.
if you're looking at a quattro make sure the rear diff lock is working by pressing the switch then checking the green light on the switch comes on, this light is triggered by a switch on the rear axle so it's a good indication all is well. if it doesn't it's probably a vacuum leak under the battery.
you'll probably find several of the switches have lights out, no big deal, you can replace the bulbs with LEDs from Maplins as long as you're a bit handy with a soldering iron.
get under the drivers side and look up at the fuel pipes, they can rot at the point where they start to go up into the engine bay, can be repaired by splicing in a new bit of pipe or replace the whole lot but that'll be mega bucks.
on most cars you find the outer CV's can cause problems but i've found inners on the coupes can seize also so give them a good rattle around to make sure they move freely.
squeeking from the rear is more than likely the hatchback, they're fibreglass on coupes for weight saving and tend to squeek quite a bit if not properly adjusted, 10 min job. the rear diffs on quattros can clunk a bit if you're not very sympathetic with the clutch, i drove mine for a couple of years then replaced the mounting bushes, hardly made any difference but nothing fell off so it doesn't seem to be a major issue
oh, and the cable for the seatback mechinism can snap, not a big job to change them and check the steering lock works when you take the key out
if i can think of anything more i'll pop back, hope that helps
