If the system is under sized (to many bedrooms) the tank will need to get pumped more frequently.The other thing to consider are roots from trees and bushes they have a way of getting into (clogging) septic lines.I would try and find out when the last time the tank was pumped, and when they recommend pumping.

. $5,500 of that was dp, closing cost and tree removal. 

If the other sewage lines pass through your lot or your line passes through other lots, then the owner of the sewage line may not be able to control if large trees (that can have roots grow into the line) are planted nearby. 

I'm looking at Joshua Tree National Park, but keeping my eye on near Grand Canyon too. 

Not my cup of tea for sure. 

Lakes, trails, trees.

I'd eventually like to go commercial, and lease out something like a CVS or Dollar Tree type of property.

However, if you were looking to set up a really sweet life in a villa by the water or surrounded by palm trees, it could make sense for yourself but not as a straight rental property.

inspections done, septic scoped, flushed, dye test, water/well tested; few issues, mostly minor, but for insurance reasons we’re asking owner to trim some trees back. 

Sometimes all it takes to "shake the money tree" is a three day notice posted on the door.