And if battery prices continue to decline, electric "motorcycles" (i.e. 3-wheeled cars) with low maintenance costs will be available for similar prices.

First you'd need enough customer traffic to fill the vehicle. There is no point in buying a vehicle that can serve 12 customers if you never get more than 4 at once.

Space to park doesn't seem like a huge problem when they're making deliveries. The mail truck is bigger than these things. Buildings with tight parking commonly have a loading zone or a space with a 15 minute limit specifically for deliveries, and it's big enough for a light truck.