Hi all.
I just got my first Audi two days ago. It's 1998 A6 Quattro with 150k. I got it for $5000 (please don't say I overpaid =)

Well, I'm actually a Classic BMW fan, but this time I needed a car to drive and came across this Audi. It seemed cheap, I took a look under the hood - it was deffinatelly neglected, sludge in the engine etc. Also oil leaks in the front (probably seals). Little valve knock on one side as well. Then the story goes "as always" I drove it and was unable to resist, so I bought it %)
I'm a fine mechanic so I decided to service it asap. Bought spark plugs, filters, new oil. Started to take a closer look and found out more bad stuff:

1) the oil is leaking from everywhere. 5th cylinder plug hole was the most full, you can not even see the plug in there, just oil.
2) seems like the oil pan is leaking as well, and oil cooling hoses too.
3) After I flushed the engine, and put Castrol synth 5W30 the valve knock noise became worse.
4) The most strange thing that it started to shift harder as well, for some reason. It's an automatic, and when I switch from "R" to "D" the car goes into gear more hard then before, the shock is more noticeable. =\

What should I do? I guess it's a good idea to replace valve cover gaskets and everything that goes with it right away,,. Also possible pan gasket as well if it's really leaking. Leaking hose connections are easy - no questions here.
About the valve knock, the car has hydraulic valves right? So the valve lifters must be replaced. How hard will that be to do? Should the valves themselves, rockers, cam shaft and so on, be replaced as well? Or the lifters should be enough? The old spark plugs seems to look fine, no sighn of trouble there.

Also what about that sudden transmission trouble? The only thing I can think about is that maybe the car was standing on ramps too long while it's -10C outside and the fluid was not distributing even when I started to drive right away?
Also some oil deffinately got into the cyllinder chambers when I took the plugs out, and the car smoked for a few seconds first, then it was fine however exhaust still smells funny =) Could the Oil and plugs change affect transmission work somehow? I also moved the car in neutral a little, coule I mess up the computer some how?

And at least, what else should I plan on doing soon. Any things that must be replaced, like water pumps and so on? The car has a timing chain, by the way, right?
Is there any specific good repair manuals to by?

Thanks for any response.