Hi Woodster,
1 - I can do routes on google and convert to GPX on mapstogpx.com then load them onto the Navigator.
Early days for me though yet with that and I have found it can alter the actual route when transferred and dunno why yet, but for simple direct routes, it works well. Must just need me to put more waypoints in it to ensure it goes where I want and not the route it may choose (faster/shorter etc)
2 - I've used a USB lead from my desktop to the Navigator which has a USB c connector. Once my google trip is converted by mapstogpx.com, I save it on my desktop and transfer it to the Nav. for use on the device when ready.
3 - Don't know that one for sure soz.
4 - Yes, that's why I liked my old Zumo550 and with the Nav, without being connected, I can enter addresses with the search function or simply press on the screen where I want to go and it drops a pin to set your route.
The app on my phone, also allows me to do that so I suppose that when I'm away and perhaps have locked my Nav in hotel room, while sat in pub or tent, I can set trip plan for next day on just my phone which connects a syncs with the Nav when back on bike. The plans from the pub the night before will magically appear on your Nav.
I'm happy so far.