We can build about 30 of them, limited by usable land for septic.

Some HOAs don't allow you to, and others have a limit as to how many in a neighborhood can be rented.Second zoning: are you allowed to convert your property to a two family.  

Let’s start with the math.Purchase price: $760,000Conventional loan limit for area: 647,000I was looking to put down 5% of purchase price: 38,000This leaves me with a discrepancy of $75,000.This will be a house hack with incredible upside potential and appreciation.

For instance you may want to limit the value of each to 1mm , which could be 10 properties worth 100k each or just 1 property worth 1mm.

Also, you are living in the property which should negate the limited liability of the legal entity (consult a qualified professional or two).Legal entities such as a LLC are not eligible for conforming residential loans. 

Not sure if its outside of the 3 or 6 years limit, but it will create another sale he/she should be reporting this year. 

Based on your limited info my answer would be sell it, but it sounds like the trust or will is preventing you from doing that.

In the area where I would like to purchase next there is a conventional loan limit of $647,000.

It seems like in today's real estate market with limited supply, it is extremely difficult to appraise or accurately value a home (especially in New England/ Great Boston area where I'm from). 

@Gary Mazzarella for the most part land trusts, which are nothing more than a regular trust used to hold title to land, have been replaced by Limited Liability Companies.Before LLCs we’re available, limited partnerships and corporations where vehicles used but each had some negative tax consequences and ongoing costs and complications.