They may have multiple depots in the larger area. Maybe spread further apart though
True! Presumably they'd refuel the vehicles in these places as well. The number of depots would depend on how much time you want to waste having vehicles driving out-of-direction and (1) the cost of additional real estate plus (2) the cost of employees at each location.
They're electric cars, so I assume they don't need to be juiced up in between rides.
The service runs 24/7, the vehicles certainly have to be out of service to charge at some point.