Web app design and developement

Excuse me if i am asking silly questions in adavance. With some friends we want to design a web app that will go in a web broser. It is a pretty huge project. For instance it will contain:

1. Sort of a social network
2. 3d avatar design specific to each person's body
3. 3d designed object

My questions is: as i am new to web programming what are the best ways to do it (architecture, development language). I read that there are several ways to do it:

1. Decompose the web app into frontend and backend (but what to put in each end)
2. use for frontend: angular js, html and css
3. use for backend:ruby on rails or rest api
4. ThreeJs or css permitsfor 3D

We are looking for some technos that will not limit our app if it grows quickly so that we won't have to re-code everything.

I have a computer science degree in embedded systems but i am familiar with databases, html, css. I need just a little hint as i don't know where to start?

Many thanks in advance