I think for something like this, until it is a proven model -- you'll be hard-pressed to find conventional financing with a regional bank and/or credit union. Private lenders may be the best solution.
To echo what someone said previously, unless you have a partner with illustrative capacity/cash to help carry this, conventional financing will be a tough ask.
What I've seen, conventional cash down for horizontal development can range anywhere from 25-35% (if not more); then when you go vertical you'll be in the neighborhood of 20-25% of that cost. You may have to swap some equity in this for a partner with capital to help get this up and running. Pre-solds are the way to go, but this is the first I've heard of something in that size, and most Banks will be unwilling to lend on something so unconventional unless you have pre-sold a good amount.
For some back of the napkin math, most Banks will want to be out of the development at no more than 75% of sold inventory (meaning if you aim to develop 100 total lots, at sold lot 75 they want their money paid off).