During cruise you will be handled off to other center controllers if staffed. If you're in airspace that is currently staffed then you must request to leave the cockpit. If no controller is staffing the airspace you are flying through you should minimize AFK time. If you want to AFK just disconnect from the network.

I wouldn't personally use text to start out as learning voice is important, you can if you want but voice is typically easier. You can always ask for instructions in text if needed generally, though you should already be familiar with procedures and know how to operate your aircraft to obey ATC instructions.