1. good car, not an outstanding deal...its a 96
2. yes, definitely
3. I know the DOHC 3.4L in my lumina had a major head gasket leak, dead water pump, 2 blown serpentine belts, and a 3 transmissions, and not the best gas milage in its 125k lifetime. But the 3.4 is a good motor, its DOHC nature, combined with lack of aftermarket support means that intake and exhaust is almost the best you can do for it.
4. see above. cost me $2200 to have it rebuilt the one time it blew out of warrenty
5. the DOHC 3.4l and the 3.8l are very comparable. relatively the same hp output, more torque out of the 3.8l and much more potential due to more parts being available for cheaper
6. 97-03 isnt available in a manual. but yes, the auto was upgraded from a 4t60 to a 4t65, HD differentials on the GTPs
7. hell no.
hope this helps.