My additions:
Look up carefully where you can / cannot jack the car without doing damage to the aluminium shell.
While you’re under it, give the suspension lower arms a good poke with something like a stout screwdriver - they rust out eventually!
Any 507 spec oil will do, search my thread on this but the headline is Mannol 7715 is VAG approved and very cheap. You may choose to buy something more expensive but there’s really no need, especially if you change it regularly
Remove the oil filter first after having first checked the sump nut will loosen off OK (just in case / so you don’t have to install a new filter without changing the oil if not and you don’t have the time / tools to sort it). This is because there is a good few hundred ml of oil in the filter housing that will partly drain into the sump once you remove the filter. You can buy a magnetic sump plug replacement from gold plugs (Opie oils sell them, they are the same for all 1.4 and 1.9 TDi PD engines) - first time I dropped the oil on Audrey with this fitted a hedgehog of metal swarf was stuck to it so well worth it.
You may find some of the engine tray torx bolts missing, you can buy them from eBay in packs of 10
Another important point to check while the engine tray is off - carefully inspect the alloy metal boost pipe that runs along the side of the sump and it’s clip! See my warning thread on this, this part is unique to the 90 model and unavailable new.
It may be worth buy a new OE dipstick from
@CreweAudi wjile they’re still available new for £13 plus postage, for when (not if) yours will break!
Good luck