I don't think a higher voltage will get you more torque, but the motor will have a higher unloaded top speed determined by it's KV rating (rpms per volt). Of course more power will get you more torque and you can conduct more power with the same gauge of wire at a higher voltage. Power = Volts...
It won't change anything for apartments that already ban ebikes. Not for many years anyway. These batteries are safer, but can still catch fire and there are still millions of regular lithium batteries out there. And apartments won't differentiate by what type of battery is in the ebike. They...
Then people will just order them directly from AliExpress or another vendor. Or if they have to get it from Amazon, have it delivered to a friend or shop across the state line. These kinds of bans won't stop it.
For long, steep climbs, you would be better off with a mid-drive motor kit rather than more power that can use the gears on the bike. 1000 watts can get you the speed you want. 750 watts can too. Even a DD hub motor will overheat on a long and steep enough hill. You can use the Grin motor...
I have a natural has generator and battery backups (UPS) on all the electronics i care about. It seems like the power goes out once or twice a month here. If it is not weather, Edison is always doing some kind of maintenance.
I don't see the picture of your bike with the mounting bracket. I am pretty sure this battery uses the same connection. I have never bought from this vendor, so I can't personally vouch for them. I have bought from EM3EV before and they have a very good reputation, but they don't have a...
A repair stand is worth buying, but for roadside repairs, you could get a set of these:
https://www.amazon.com/dp/B0CM7JHNFB?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_5&th=1
That looks like a tiger shark or dolphin case. If you don't mind replacing the mounting bracket also, you can buy any new 48V battery with a new mounting bracket and splice in the connector from your controller with butt connectors or solder/heat shrink tubing...