The metric to measure whether it works or not is the CONVERSION RATE, not whether or not a deal was made.If your conversion rate is 0.03% (like it usually is for DMM), spending more money to get more mailers out does NOT change the effectiveness of that strategy.

I'll for sure need an architect and lawyer amongst other players.

The “tales” of nothing down/seller subordinates “down payment” done successfully almost always hide the most important information - that the buyer either provided additional collateral (such as real property owned “free and clear”, a certificate of deposit in an amount greater than the down payment required, or the buyer is financially strong enough that part of the financing was in effect a personal loan or line of credit. 

If separate, is GP taking the 20% split + their share as 10% LP or does 20% include their 10% equity (effectively equating to a 10% GP bump)Loan guarantor fee and dispo fee is a little higher than I have seen many other deals.  

My rental is in Upstate NY and I have a great lawyer that I could refer to you who could help you draw up the appropriate lease.

It is a business, so run it like one, as @Tom S. said, start the process and follow through.Unfortunately you're in a Blue state so this will be more difficult for you, so yes get a lawyer if they don't respond immediately to your 'pay or quit' notice.Don't take any more partial payments, that will delay your case!

First of all - most people (including real estate investors) are lazy and will always gravitate towards promises of quick returns / passive income promises.But also - what you are describing is something that AirDNA does extremely well and automated - it can be a little pricy, but way way more effective and accurate to do this with that tool - highly recommended

I would also like to know what effect business structures have on taxation (LLC/ LLP/ LP).

How do you think this will effect rental rates , home sales ,  construction costs , and insurance costs in Florida and up and down the coast  ?   

Consulting with a lawyer or a CPA familiar with multi-state real estate investing can help clarify your specific situation.