My state lets you register hand built and other oddball vehicles - basically, if you can get it past customs, you can register it. The out of state inspection for a title transfer is to check the VIN.
Insurance would need to be from a specialty provider who do insure oddball vehicles. Someone I know (in CA no less) insured his homemade electric motorcycle this way. (It’s titled as the chassis of the BMW regular motorcycle it was built from.)
If you’re pulled over, you would need to show things like seat belts or turn signals and so on. I got nailed for not having a shoulder belt in a homemade vehicle made after 1960. Seat belt ticket was my punishment, although the cop remarked that adding a shoulder belt would be a good idea.