Not bad for no owners manual yet. You are correct that it went in regen. Since its the older series XR4046 it will do so about every 5 hours. Usually you can continue working while it does its thing. I keep the RPM 's up to about 2300-2500 during the regen cycle.
You also figured out part of the parking brake. It will beep if you shut it off without setting the brake, it will beep if you get off the seat with the tractor running and didn't set the brake, it will beep if the brake is set and you start to move the tractor with the HST pedals. (Not sure if you have HST but I guess you have the gear model as you didn't mention it)