Well you're not starting simple. Yes you should go modular, and you should go procedural. I used cityengine once, dno how it is these days. Studios tend to make their own solutions based on houdini, but there are other softwares and plugins around.
Houdini is great for procedural content like this. You can plug it into unreal and its pretty awesome. https://vimeo.com/228234352 Depending on what tools/engine you are using there are a few different options out there. Are you using just Maya or Max? Are you using an engine like Unity or Unreal?