Look up comparables and come up with a real After Repaired Value.

Clearing land/leveling a lot costs are small compared to the whole build so it won't be enticing for a builder to split his profits, Amazon plants/fulfillment centers are popping up everywhere, won't have any affect on the market. 

We don’t know any PMCs to recommend in the area mentioned, but since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

On new constructions in a fairly new area, how does property get appraised up to contract if there are very little or few comparables around?

Hi Napat,Make sure you are comparing Apples to Apples.For instance is the Contractor going to use Owens Corning Synthetic Underlayment, or X mil plastic sheeting or tar paper, or nothing because he believes (for instance) hail damage is less with nothing under the shingles, and the Ownes Corning guy is going to use the Owens Corning Synthetic Underlayment (???)

All add by saying start talking to lenders, you can start comparing the different products and requirements to get qualified.

Worst case scenario is not being able to refi unless I come up with $50k.Austen Mueller, I tried using the duplexes and square footage to formulate the value of my 4 plex but was told that they do not translate and they would only compare another 4 plex.It seems like I may have to walk away from this deal. 

Your best bet would be to contact a local bank where the mobile home park is as they're more likely to lend compared to a nationwide bank not familiar with the area. 

Start with no less than a 4-plex because when you increase the rents for a 4-plex your profits are almost exponential compared to a single-family home.

A good rule of thumb is to compare the extra 5-10% down you are doing and the monthly payment with the higher interest rate.