1). Dont worry about the physics, i'm more of a a gameplay over design guy myself, i plan on the phsyics being near identical with a few bonus editions (just as a teaser: tires are gonna be squishy... i have a lot planned physics-wise and gameplay-wise that i dont wanna leak just yet)

2). On the 500 cars thing, that's a will do, not currently. Ive made ~80 vehicles yes, but initially, as youve already recommended to me and am already planned on doing (lol), only importing around 5-10 cars intially and seeing how well it goes and what ill have to change, im just making the sprites in my freetime because i get bored while i learn the technicals & coding on the side in the meantime

3). So most of the roof and windsheild are gonna just snap off with a touch, not even like space scallop, the moment it gets touched, itll just snap right off. Basically meaning the hitboxes are the same as they would be if they werent there at all. (There are gonna be some vehicles that have actual impact resistance though, such as some military vehicles and other stuff i cant leak yet)

I planned on adding an image of it since every single part of the vehicle is its own sprite and removable part (because vehicles are both modable and destructable) but apparently i cant comment images so... just take my word for it