You may be able to find some loan product where the lender would allow you to pledge your current projects as collateral for an acquisition loan.  

Collateral is the name of the game

Pawnshops love taking womens shoes and jewelry as collateral to make mortgage payments. 

Regarding collateral and cash reserve, does 750K seem resonable?

Seems like that's not an emergency today,But that depends where you are, it can be an emergency that has economic impacts.Banks generally don't have issues with issues that won't impede collateral values over the term of financing, so you're looking at 30 years.My more immediate concern is that if I were buy property to be held for future generations, my great grandkids, I'll look to the elevation and location, I doubt people will be born with gills in a hundred years.That means I'd not be buying in Miami, D.C., Lower Manhattan, or costal inlands.Before my properties are at risk, the State of Arkansas will have beachfront property. :)

When I sold it I didn't pay off the mortgage, since the Corvette was not the collateral. 

I need to try to stay within Bigger Pockets guidelines.Our company is a nationwide consultancy to lenders, and those who want to be lenders, engaged in purchase money finance of manufactured homes using the title as collateral for the loan.

My worry now is with my lack of experience in MF investments, taking on a large deal (as much as I could afford) seems high risk to me, especially if my equity from SFH is on collateral.

At the end of the day though, if anything happens, they will have the house as collateral so I don't see an issue with it.

You could, if you wished, get a cross collateralized commercial loan too.