Nice buggy to start with I think. My first nitro was an inferno 7.5 when they came out. As far as straightening the main chassis you would be better off looking for one on ebay. You can find them very cheap, probably like 30 bucks. The bent one will do more damage than good, I know cause I tried. Bigger tires would mean changing the gearing and I would not suggest it. Too much stress on the moving parts of the drive train and engine. Cant speak to the engines you mentioned as I have never owned either but here good things about the nova. Either way have fun, find a track or good LHS to help a bit with the tuning and read the "tuning bible" at the top of the thread list. You will be quite happy with the buggy, it may be outdated but it is tuff as nails and easy to work on and like I said, parts are all over ebay cheap! I just rebuilt mine(new chassis, brakes, bearing, diffs, shocks etc) for less than 80 bucks and sold it. And check out infernosonly.com they have tons of info for you.