Going DIY, with the right engine, you'd be surprised how good your results can be. With UE4, Blender, Gimp, CG Textures, BlendSwap and MakeHuman...etc, you can make a decent prototype. But you would need to spend a lot of time with tutorials, I'm afraid. Considering you want to make money on this project:

1). Go to CGTextures and find the textures which closely resembles your vision as much as possible. Use GIMP to generate normal maps, colour maps. specular maps...etc.

2). With regards to collision, I don't know what engine you're using but you can make collision using a convex hull or separate cubes at a time. I'd suggest that your prototype only includes something which has very simple collision, for example an inside of a building. UE4's collision system is very beginner friendly, you can even make the collision in the editor itself.

3). Narrow down what you can do well in your game and focus on that. You need to wow the investors and 1 polished level is better than 5 unpolished ones. Are you a good writer? Show that off in your demo through your NPC interactions. If you don't have a specialty (yet), then I'd suggest to hold off making a game until you excel in at least one area of game development (and that can be built upon, by joining mod teams).

In that case, I'd strongly recommend getting good at world building. It'll be the first thing the investors would notice on the crowdfunding sites. I know quite a few mod teams who need help in world building, mainly for Skyrim.