yes, a map-overlay in the editor will be possible, but we built the streets, buildings etc. in an external modeling program. Spline-Based/procedural In-Editor "modeling" wont give you the details needed to recreate many spots.
About buses: For the most people, who probably never worked with Unreal Engine, no, it wont be very intuitive, atleast not for the first couple hours, like in every other new program/tool. But as soon as you understand the basics and what does what, it is, or becomes quite intuitive. Learning curve in Unreal is quite steep, and we´ll try to provide tutorials covering the questions.
Any modeling software that can export FBX, OBJ, DAE and some other can be used, so yes, you can use Blender.