Technically my ROTH 401(k) is not me but a different separate tax entity.Thanks for the answers 

Anyway my question is can we rent out the basement to someone as a separate unit from the upstairs without it being a kitchen?  

I am not worried about the accounts "becoming a community property" in case of separation or divorce.

In our area, on a multi floor property, either two separate systems are required or zone control with a single system.

should I build a wall and create three separate units?

Also, would I need a separate bank account for the rental income collected?

The comment "at the personal level" only applies if there is separation between you and another entity.

That may mean buying materials or paying for them separately to not allow them to 'get ahead' on money vs work.

Multi tenants are almost never responsible for the water bill and, depending on the neighborhood and the HVAC systems in the building, the owner may be on the hook for paying to heat the building as well (Is is one central system like a boiler, or separate like forced air or electric heat?

You can absolutely do it and I would recommend you get 2-4 units or at minimum a basement to finish out as a separate area.