1/ It's not weird to live near parents, although living with is rather strange as an adult (until they move in with you). I know lots of people who live near family, including at least two instances of people buying a home next to their parents. Heck, I live 14 blocks from where my Mom grew up (although she no longer lives in NYC).

2/ Probably more than most, but I also have business in that town. I'd say the average is 1-4 times/year with a mean of two for holidays.

3/ Not a big deal and basically no bureaucratic overhead. Either way you'll probably need to go on over to the DMV to register to vote, but a new state will give you a new license too. Can be done in an hour or two and doesn't have to be done immediately. Culturally and logistically, as long as you're moving to a similar neighborhood (e.g. middle class suburb to middle class suburb), there's basically no learning curve. Buying a home, renting an apartment, setting up utilities, and registering a vehicle are all the same process wherever.

4/ Very common to marry inter-state.

5/ Probably less than people assume. Once you get past the top ~100 colleges, there's almost always an equivalently good local school that will cost less (in-state tuition). Many of those top schools are also public universities which tend to favor in-state students in admission (note the high percent of CA residents at places like Berkeley or UCLA). I'd guess work and desire to live elsewhere are bigger factors for people moving. Then again, I have no data to back that up so take with a grain of salt.