The tools you need, given you do not want to start at zero (and write your own engine) would be: a 3D Package (Blender (free), Maya (lt version is not too expensive), 3DS MAx, others) to create the building meshes, a game engine (Unity Free version, Unreal Engine 4 (both free)) to create your scene and run the walktrough.
Preferrably you have some helper tools to extract the geo data and create the rough scene for you... this is not my area of expertise, but AFAIK some tools like that exist for the Unity engine, grabbing data from Google Earth and creating terrain, or even city geometry for you. No idea how far this will get you, and no idea if anything is free.
MAYBE there is a tool for Architectural pre-viz that can be used instead of the game engine. This tool will be much less flexible, and I don't know if there are free ones, but maybe worth a look.
The skillset you ned includes:
- 3D Modelling skills: Creating meshes, creating textures, UV Unwrapping, how to optimize meshes for realtime rendering.
- Game Engine Editor usage: you need to know your way around the editor of your chosen game engine... hardly rocket science, but will take you some time to get over the first bump of the learning curve
- Programming: Yes, you will need some programming skills. At least if you go with the game engine, not much, as your requirements are pretty basic. Just enough to let the user conduct his walktrough, and create the needed menus to select the era (Time of day, whatever you else add in options).
I am not worried about the project management details at present, but just investigating the direction and approach of such an initiative.
It has been done before:
and won an award.
Your other pointers are excellent, thank you.
