This will help you to complete larger chunks of rehab at a time while also letting you leverage your cash should another good opportunity for a project come your way.

I would recommend you either purchase a single family residence (SFR) and rent it out. 

Good Luck!

We've decided to make the new construction our primary residence after the purchase.

Yes I think everything will depend on the apprasil but that's a good point on 2 adus on single family residence zoning.

In your proposed situation, here is what I would do:1) Make sure you have a good/solid/reliable contractor that can actually do the work and has capacity to handle the project.2) Apply for the max HELOC and get it established. 

Thanks Jackson, good insight!

As long as you intend to live in the property as your primary residence, then a primary residence mortgage is appropriate.

A good contractor can give you a best-case, worst-case estimate.

If you need a good HML just DM me.