I looked at an 01 Boxster today with 156k miles, asking price $9000. I'm not sure what to think. It's the first Porsche I've ever driven. It seems decent, body and interior are in good shape, handles well, drives well. But I need your expert advice. I know nothing about boxsters beyond what I read today on these forums and on the websites in the sticky thread for first time buyers. However, I do know cars, so don't be shy with technical answers. I've done everything from ECM tuning to engine and tranny rebuilds, turbo mods, etc.
So the worst thing about this car is an engine vibration at 3k (2.5k to 3.5k at most, goes away outside that band) that makes the whole car shudder/buzz. Everywhere else the engine seems smooth enough. This happens when revving at a standstill, or driving in gear.
Could it be due to bad motor mount(s)? At least one is definitely shot - it has the characteristic clunk when shifting briskly.
The gas gauge reads empty when there's gas in the tank. Is this almost always fixed with recalibration? Why does it get miscalibrated?
What are the chances of RMS or IMS or other terminal engine failure if the car's survived for 150k+?

I'm not poor, but I definitely do not want to deal with engine failure. This will be my girlfriend's daily driver.
Should I just walk away, or run, while I'm ahead? Or will this car likely run to 200k+ without major issues? Some cars run past 200 without batting an eye. Is the Boxster one of them, or can I expect a linear or exponential number of problems with age? What fatal signs can I look for, other than oil leaks, oil in coolant...? What compression numbers should I be looking for?
Thanks, and sorry for the newb questions. There's only so much information I can absorb in a few hours

I know there's a million questions in this post, but please try to answer as many as you can. Thanks again.