The definition is pretty much arbitrary, but it's generally considered the point at which the atmosphere becomes too thin to support conventional flight. In Europe it's considered 62 miles (100km), NASA considers it to be 50 miles (about 80km).

Geography would have a very negligible effect at that altitude. It's a fixed altitude above sea level and doesn't fluctuate

Nope, Blue Laws

No worries, we all goof

I never said one couldn't

If you think playing GTA will prep you on how to rob those places, knock yourself out. And if they let you have computer access in prison, be sure to let us know.

Because it is unnatural. Moving in zero gravity means you have to be deliberate and careful in how you move since you're used to having resistance (ie your feet on the ground) rooting your body. Moving one body part moves others you aren't used to because of that.