I have no experience with Unity. Can you please explain the kind of work involved? (btw I have no interest in gaming, but am interested in all non-gaming things you could possibly do with 3d-modeling, Unity, etc.)
Dealing with interchange formats(which Maya and 3DSM excel at, no idea on C4D). It's very common to find that something you've build in your authoring package doesn't import cleanly and figuring out why can take time. If you bring animation in at all you'll have to deal with skeletal rigging, and then the tooling you want to build around interaction on the unity side of things.
There's a reason that games budgets end up running very high unless you're dealing with 2D/simplified content.
There's a lot of optimization that needs done for realtime.
For any given asset you may have a pipeline like so:
Sculpt hi rez model in Z brush > create low rez model and retopologize (can be a very manual process) > UV unwrap and bake the high rez details down to Normal maps for the low rez mesh > Use DDO or Substance painter to create custom textures for diffuse, metalness, etc > Rig model (if you are animating it) Then export to the engine. Rinse and repeat based on major art changes.
There's a reason that games budgets end up running very high unless you're dealing with 2D/simplified content.