Congrats on the new ride. I personally have not had the dreaded parking brake failure however I’m sure it will happen at some point. Unfortunately being a powered system vs a manual park brake the possibility for fail rate is higher but not something I would be overly concerned about in the sense of being stranded provided you equip yourself with a little know how. I would suggest going on line to watch a couple videos of how to temporarily disengage the park brake at the rear wheel, not difficult and at least if it does it again you can get yourself home without the need of a tow truck. Just bare in mind once disengaged it can roll so be sure to chalk your wheels.
As far as your battery issue it should not be dead after sitting for two weeks. However that is also contingent on the battery being good to begin with. If your battery was not fully charged to begin with when you picked it up then yes, entirely possible it would have needed a charge. Also, batteries can develop a bad cell which effects overall performance and ability to store a full charge so you could also have a poor battery. See what happens going forward, if it does it again after sitting for a couple weeks after being charged you may have a bad battery. Less likely your charging system is an issue. Using a battery maintainer is never a bad idea if sitting for awhile, batteries are always discharging even when not in use.