I asked him for some criteria so I could look around, but despite having strong connections in that state: realtor, builders, investors, PM etc, I’m not sure what I can do.

Plumber, Electrician, carpenter, builder, Zoning Dept, Planning dept, insurance, RE agent, attorney, etc. 

Are there pre-published cookie-cutter plans I could buy and then provide to a builder?

Does anyone know any reputed builders for a new construction in Dutchess country area in NY.

BTW, the builder hasn't even started digging yet. 

What is the best way to get the plot into my name from my partner in order to have my builder start construction.

Even large tract builders are now constructing "rental SFH communities" so they can capitalize on year-over-year increases as well as in property appreciation.  

Generally in our area you can 1. survey into lots and then sell at a wholesale price to builders and they shoulder development cost. 

They have a select list of builders that they work with, which continues to grow, so that will limit who you can have build your tiny.

Go over to Reddit and post these pictures and description on r/Whatisthis/ - you should have an answer in about an hour - probably by either an engineer or sales rep or home builder that dealt with the things daily 30 years ago. :-)