Then wherever the water is getting discharged off of the roof, that what water is getting at least 4-5 foot away from the structure before it is left to drain with gravity away from the property. 

Water- Either check with neighbors, drill test well, or call me to Witch water to see if you have water on the ground. 

Added a new cistern for water and added a shop bathroom in addition to completing the apartment.

At one single family house there was an oil haot water boiler with domestic hot water.

She says that if she turns the flow low though the water does start to get warmer but it never turns hot.

(that policy was cancelled by the carrier and I will be getting a separate policy)2 hail damage to Tennessee property  and water damage due to storm (claim is in process) Another Tennessee property now has had a water pipe burst in the kitchen ceiling and flooded the whole house. 

Mold requires two things to grow: water and food (dust is sufficient food).

Should I provide my guests with bottled water or a Brita water filter or leave it up to the guests to bring their own water?

Opex has been a huge hit to most property owners in all shapes and forms, myself included, but to know to keep your back wide enough to cover your own you'll be able to navigate these waters just fine. 

Your best bet is a property on water and sewer in a non HOA community and either convert the garage to an ADU or Build a separate ADU .