This is one of the main reasons why I partnered with the "LOI Events" group.

Come to find out it appears the sub contractor he hired (the squatter) is the main ********ter in all this mess.

Is there a "sweet spot" distance from a highly, mainly urban area?

It has proven to be more difficult to set up than expected mainly because of having to use a third party company for a physical business address1.

If its on the same parcel still as the main property it would be appraised alongside with the home - typically not taking full credit for rental income but more of additional square feet/space to the property. 

The main house has 3 floors.

Even though you'd be getting into the deal with $0 down, you should still have enough cash (or availability to access cash) to cover the worst case scenario of a tenant who immediately stops paying after you close on the property and requires you to complete an eviction action against them.To your second question, I'm sure you've heard it before, but the 4 main ways you make money in real estate are cash flow, appreciation, debt paydown, and tax benefits/depreciation. 

My name is Jenny Cunningham from FL, I started investing in real estate about 2 years ago with my partner (male) and have mainly focused on doing flips while recently looking to get into the rental market as well.

Just run the line to the ADU, and then trench the rest of the line to the main house.

You could also have a window AC unit on hand, that you can place in the unit until the AC Tech gets the main air conditioning system repaired.