Can't say what's hardest, too many moving parts but take care of your tenants and build that goodwill, pays off in spades.

Definitely tread carefully here to avoid any discrimination claims!

You can still use a property manager for on-site tasks, but your own activities—like managing bookings, marketing, and bookkeeping—must be well-documented and exceed the property manager’s time.It’s important to carefully track your hours, especially if you’re managing remotely, as this can face additional scrutiny from the IRS.

Beyond carefully vetting the tenants, how can an investor protect themselves from squatters if we want to sell years down the road?

But honestly I don't care how many courses you take you must have a local team or you will crash and burn.

Far too many parks just 'give' a resident in the park free space rent to keep an eye on things and do light maintenance with no 1099 reporting. 

Be careful.

You could do something like what you want if it was your personal primary residence and even then the interest rate would be ugly. 

A reliable tenant stays for many years, pays the rent on schedule, and takes good care of the property.Reliable tenants are the exception, not the norm.

She would be putting all the cash down for the property and I'm a contractor and would take care of all of the rehab work along with finding the house, dealing with real estate agent etc. how can we make it so that it would be 50-50 ownership of the property and all future profit?