The house has a really nice floor plan that I spent a lot of time drawing with an architect, and I'm really happy with the way it turned out.

@Brad ArmelYou need to have a gc or an architect walk thru the place with you to help define what really needs to be done. 

The flip will take 10-12 months according to my architect/contractor.My question is what kind of loan would work good for my situation to cover the other half of the flip cost?  

Mini-splits would be a good choice here (no ducting required).Call an architect, they'll come out and look and give you ideas....

Often times you can find a local architect or going on "Upwork" to find someone that can model out the addition you are looking for and get permit docs ready to submit to the city.Hope this helps!

I have a lawyer that has done many it's a process that includes the DOB, the Attorney General, your own attorney and an architect but if you can get it done the price psf is worth it.  

Or consult with a local architect.

Regardless, a good architect should be able to make it happen.

Then you'll want to think about hiring an architect and expeditor/land use consultant to kick-off the lengthy entitlement process, and of course how you'll finance the entire project.What is the lot you acquired improved with?  

I'd take an architect designed prefab over site built any day, not accounting for impact/regional materials "going green" ideas.