I'm also considering a separate living room space or maybe some kind of artist studio. 

You could convince people they should have their kids, parents and/or grandparents live in their houses with them. 

Real estate investing has been a passion of mine for time with my mother also having invested early on where I likely have gotten the love and desire to follow similar foot steps.I have taken last 6 months to educate myself and currently own a single family home as primary residence and would like to expand to multi family properties (2-4 units) for additional stream of income, not to mention potential tax benefits for long-term investing.Based on current living situation, I have a fair amount of equity established in my primary residency along with having enough cash to either pay off house completely or use towards investing in a multi family property.Given that I'm the sole source of income for our household with my wife being the home maker for our two kids under 2, trying to weigh out risks with getting started now or perhaps waiting. 

A new outlet/outdoor shopping space.  

I was going to do this, but I changed my mind after talking with my target demographic (my kids).

Are there any specific clauses I should include in a room-by-room lease for a shared living space?

It's a good sized house (3000 sf) for the number of bedrooms (4), especially since it doesn't waste space on hallways and things like that. 

Last night, I heard an inspiring story about a mom who brought her young kids along for a 45-minute drive to tour an investment property.

Quote from @Jerome Morelos: I recommend converting an existing space, like a detached garage for example, rather than building from the ground up.

Quote from @Bob Avery: I don't recommend leaving a space blank because someone could later attempt to add something in.