To add a dealership to your simply place an additional Dealership blueprint (BP_Dealership) in the scene. The dealership blueprint handles all the logic necessary to spawn the selected bus for the player. Make sure to add barrier around your dealership area, without it players will be able to drive of the lot without paying for the new buses.
Depots can be similarly added by placing a Depot_BP blueprint into the scene. The placement of depots is more particular, than the placement of dealerships. NPC drivers need to be able to find the leave the depot. If you select the depot you will see a couple splines connecting each bus bay to a position outside of the depot. Those are the paths NPC buses will take when they exit their bays. Make sure to place the depot so that those spline points are on the street next to the depot.
You can add a paintshop by adding a paintshop blueprint (Paintshop_BP)
All player buildings have a name variable, this is the name that is shown when one of the player buildings is hovered in the map menu.