Ultimately, it sounds like the decision would depend on the interest savings you'd get.

Sounds like you've got it covered, but if you have still have built up PAL, that is great for offsetting your tax liability when you sell. 

Your experience in sales and market insight from your work and living in the Detroit area sound like valuable assets.

Once my construction is complete, can i do an immediate cash out refinance on both properties to pay back the HML and recover my initial down payment?

Lennar is either 1 or 2 in size in the US DR Horton is the other.. they are production builder so yes quality is not their hallmark.. price is .. 2. wrapping the mortgage could certainly create an event of default with Lennars lending arm. there by trashing your credit. 3. if your buyer stops paying you have to keep paying and foreclose and hope they have not trashed the home when you get it back.. like all things creative finance wise sounds great on paper and is great if it all goes perfect but lots of things can fall apart if things do not go right.. so what is your fico score worth ?  

You really need to learn your septics operational health, which is difficult given that it's completely underground!  

I’m looking for something with 0% interest in the first 12 months and a large enough limit to complete a cosmetic flip.

That all sounds good. 

@Alan Feldman thank you for the sound advice sir!

This is a very complicated project and it sounds like it may be your first one.