Few questions from newbie!!

Votex - you can get them at the dealer but be prepared to pay up to £1000 for the full kit! Ebay is your best bet but they pop up very rarely! I was lucky to get all my kit from ebay for fraction of the price but I ended up selling the rear splitter on here!

19" - mmm i think my rims are 8" wide which is max as they are about 10mm away from the top of the coilover- the car is lowered around 45mm all round with no rubbing issues apart from full lock at the front

xenons - might be tricky and you will probably need to use VAGCOM but you will also have to install the headlight washing system to have them legally on your car. another option is to purchase a 6k or 8k HID H7 kit for the a3 - i have this and works a treat with no problems at all and MOT passable!

Other things to look out for in the a3 are....

Slippy clutch - accelerate in 4th/5th/6th low down the revs and see if the clutch slips

Look underneath the engine on the passenger side - you may see an oily stain or goop gathering at the vents, this is quite normal but if it is excessive, maybe it isnt for you

Look directly under the drivers seat under the car - there is a smaller radiator, this is the deisel cooler and sometimes its holders break - mine did the other week. check to see if its still intact or give it a wiggle.

go for a drive eithe ECON on and see if the car mists up dramatically - pollen filter needs changed if it does

when sitting at idle, the car WILL judder quite badly, this is to do with a crappy flywheel design. some A3's had a call back to get them replaced so if its really bad, get that checked. as far as i know you should have a Sachs Flywheel installed

i think thats but if i think of anything else i will let you know!