The title does have a lien but that will be paid off with the seller's profit (not sure if that would add on). 

@Jonathan Tremblay They are technically 2-1, but there is also an office that my tenants have used as a bedroom (the office doesn't have a closet and doesn't have room to add one).  

- Are there refinancing strategies (a-la-BRRRR and forced appreciation) I could leverage to help finance the addition of an ADU, assuming we do add one?

Dollar wise what kind of vaule does a 2 bedroom becoming a 3 bedroom add on Long Island.

You may also get a break if you add-on to your title policy.

Personally, if you plan to do the work, but have a regular job, add on a couple of months to complete. 

If anyone has any more information that I left out, feel free to add on.  

Now I may add one more thing.

I realized that a lot of the clients do not live close by or even in the state and would need someone to care for their property.I decided to start offering small services that would be just for the Airbnb such as supplying toiletries (toilet paper, paper towels, soap, shampoo etc), welcoming gifts for guests, meeting the guests to deliver the keys to them, and also lock out service in case the guest loses their key.We realized the demand was high and decided to add on more services.

I'm presently negotiating 13 MLS deals in Cincinnati that I believe are priced below where they should trade to me, not including any fee I'd add on top.