Todd - I saw your other thread, and the car you are looking at does NOT have the sport package (ZSP). FWIW, most of us here would give up all other options for the sport package, in large part for the much better seats. ZSP also comes with nicer wheels (staggered 18" 225/255 style 162), a tighter and lower suspension, a nicer steering wheel (smaller diameter and thicker), and a higher speed limiter (155 mph instead of 130 mph, not that this matters in the US!).
You should have a decent choice of 330i models available, so if ZSP is important to you, as it is to most of us, I wouldn't settle for non-ZSP.
To answer your questions:
1 - For tires, I don't have any major problems with the Potenza 050A RFTs that come with ZSP. The non-ZSP tires (Turanza RFTs) have a poor reputation for uneven wear and road noise.
2 - No issues in heavy rain. Traction and stability control helps a TON. A/S tires are fine, but a compromise. They aren't great when the weather is good and aren't great when it's bad. IMO, it's well worth the minimal pain of keeping two sets of wheels, winter wheels for December to March, summer wheels for the rest of the time.
3 - No real major issues with this car. Read the "ticking engine" thread for a problem with unlubricated lifters that has plagued some 325/328/330 vehicles, but that doesn't appear to be a widespread problem like the fuel pump issue on the x35.
4 - Warranty covers everything. If you can get CPO to extend to 6/100, damn right, you should get it! I doubt the dealer can just throw it in, though.
5 - You should get 18 city and 30+ highway, not even trying to drive lightly.
Take a look at
the 330i thread for more info, links to reviews, and general love for the car. This is a very fine car. I could not be more pleased with mine. But I would again caution you to consider looking for one with ZSP, if that's important to you.