Congratulations on the purchase and welcome to the site, I hope you enjoy it. I love the Si rims and I am looking forward to seeing photos of the conversion. I have thought about doing that myself, but will likely wait until my current tires are worn through to lessen the financial burden.

If you do a search on here there are dozens of threads with tips on how to maximize your mileage, 28mpg seems low even on a fresh engine, but your mileage will improve after the engine gets a little broken in. Where do you live? Weather makes a big difference in the mileage of any car.

Many here run their tires at the maximum recommended pressure on the tire. Tire wear shouldn't be much of a problem if you keep it in the range suggested by the manuf. Good luck