Your potential profit from renting is non-existent. 

Here are some benefits that you may be missing out on.When assets are removed: Are You Still Depreciating Non-Existent Assets?

If the existing pipe has settled in a low spot then it will need to be trenched.

You will not have the existing power supply that I assumed.Still I like @Jill F. idea of installing mini-splits.

MelvinPerhaps you can BUY their property from them on WRAP Around financing basis You pay them on a WRAP AROUND Note (eg. perhaps $1.00 over their existing loan balance) of where they can LEASE the home you and also give you an option to buy SUBJECT TO their loan if or when you exercise the option.

@David SwitzerThe ADA Guidelines do allow a steeper slope than 1:12 if the site conditions of an existing building can meet the criteria.

Couple of thoughts, if you think the property is worth 650k now, I would reach out to your existing loan servicer and ask them for the PMI removal form.  

Does the proforma include "potential" non-existent units?   

Sell or refinance the property to clear the existing loan. - As mentioned above.

I am starting a park that will end up with roughly 20-25 lots on plot of land that's roughly 20 acres (including an existing 4/2 house).