It is not your responsibility to house this person's items indefinitely in your rental. 

It depends on where you want to live, income, personality, and other factors.You could buy a large home and rent out the individual rooms to cover expenses, but this comes with problems.

To establish a 50-50 ownership in both the property and future profits, you'll need a formal agreement outlining each person's contributions and rights.

Offered to intern/work for him at half the pay as his personal assistant if he would teach me everything he knew.

Average person can't visualize how to fix it, but you can (create an extra bedroom for example)3.

That is a great place to start, as well as hitting some local real estate investor meetups so you can meet some other house hackers in person who have done what you want to do.

Explore my personal favorites, Set For Life by Scott Trench or The Total Money Makeover by Dave Ramsey, for invaluable financial insights.3.

What I've seen is that when asked to provide an assurance that a loan wouldn't be called because of a due on sale clause being triggered, the lender customer service typically just outright says it's not allowed, or default to a "no", because they see it as a black and white question, and miss why the due on sale clause is actually written into the mortgage document to begin with.If one is transferring property title from personal name, a Grant/Warranty Deed would be drafted/recorded to transfer title.

I am not sure what type of real estate investing you're considering, but it sounds like, with your family and busy job, you won't have a lot of time to be hands-on or personally involved. 

Many are personal friends of mine living just 40 minutes south here in San Diego.