1. Hasn't been confirmed but honestly, it's always came out for the PC.
2. Vehicles, yes, and maybe some landmarks but they'll be in different areas. This Liberty City is completely different. There will be references to past GTA's though, yes.
3. Hasn't been confirmed, and my guess is probably not.
4. Hasn't been confirmed either, but Rockstar said they want more realism this time, and obviously adding a jetpack isn't realistic. So again, my guess is no.