I am new to diagnosing the car- but have learned a lot here and having done a lot of work on mine - 97 A4 2.8L v6 FWD. That being said... you do not mention what the oil temp issue is (unless I missed it). If you are referring to the gauge not working (showing the temp) I have the same issue. I was told it could be the gauge or the sensor itself. After I had the car put back together I realized I forgot to change the sensor and when I found out where it was I was not going to put the car in service position just to do that. In your case the senor is probably in a different place and change that and see if that fixes it before first... I would check the oil filter housing/flange to see if it is there. You could do it when you do the timing belt.

As far as the oil leaks.. my car leaked lots of oil.. The previous mechanic who worked on it said it's and Audi and old. When I decided to work on the car myself. I checked the camshaft/crankshaft seals (no leaks) when I checked to see if I needed a timing belt. I replaced the cam plug (it was leaking very little). The leaking was coming from the valve cover gaskets. What I found when I went to remove the covers was the idiot mechanic had tightened the valve cover bolts so tight (estimated at least 20ft/lbs) it rendered the gaskets useless. After I installed new gaskets and tightened to 7 ft/lbs (specs) I have no leaks. The only small drip is from the rear main seal.. to be done when a clutch is needed. So I would definitely check the valve cover gaskets and other cam seals you might have.

 

Oil issues on any car are often thought out to be big issues. To put it simple, if you car is burning oil then yeah it most likely will be a pricey fix, if it leaking oil, then in most cases is a simple fix as it may be leaking from any gasket/seal/pipe/sensor which all are relatively cheap to fix. Be more worried if you car is burning oil and not leaking oil.