1. Can I safely put a Shimano 11-speed quick-link in the chain? (It is spec-ed at 105, whose chains don't have that by default).
I would think it is the same as any other chain setup yes.
2. Can I lube the chain as with a standard bike? My preference is to use wax, but if that is problematic, I can do something else.
Yes
3. Is it bad to re-charge the battery when it is above 50%?
Bosch has online manuals, but yes you can.
[QUOTE
4. For climbing hills, the pedal assist appears to reward the rider for climbing in a higher gear. Will this damage the motor? (We are talking 7 to 15% grade, average 10%, over a couple of miles).][/QUOTE]
The Bosch motor has thermal sensors. It is unlikely that you would damage it. Most likely you would notice thermal rollback.