I am planning the structures to be low-end to mid-end duplexes, triplexes or fourplexes that have a unit size of 900 square feet to 1,000 square.Any input is appreciated.

The IRS doesn't seem to care which method you choose but it must be reasonable and consistent. 

trust deeds non judicial. so like in GA and MS  which is trust deed country or in GA its called a Deed to secure debt..it can be quit fast 90 to 120 days from filing the NOD .. in mortgage states and particularly NE states the process can take some time but usually at least one year.. to from what i have heard in NY it can take 3 to 5.. borrowers and lenders can also stall things out a bit using different methods.

So, I want to do this deal, but I am concerned about how to structure our agreement. 

But I haven't seen many, just few different methods, e.g. four or max five.

Like conventional income properties MHCs have their own class structure ranging from D to A.

The valuation methods are:  Actual Cash Value, Functional Replacement Cost , Replacement Cost .

The next one is April 9th.If you still have no takers after you've tried to sell them via the above methods, then you definitely have a price problem, because there is no shortage of buyers for the type of properties you are describing.

I do my own estimate based on J Scott’s method, along with having my GC walk the property with me.  

This will vary based on how far your structure is from the connection but a rough estimate would be nice.You may want to call the public works division, I imagine they have to hookup the actual connections to the city service.