You should be doing a full home inspection to include radon testing and termite check, a sewer (or septic or well) inspection, and if applicable, an oil tank sweep.

Have you tried to sell a few just to test the market?

Key is to keep your transaction documents on file and document the transaction path for your CPA tax preparer.4 of the lots have sold in the last 2 months. 

Just want to be prepared for the inevitable.

So, the rate will be probably ~1.25% higher.Don't forget that there is another requirement about being able to carry the mortgage as if the other units weren't rented -- forgot the formal name for this "test." 

They didn’t seem interested with my original offer but I am meeting with them this weekend so I’ll be prepared to go higher.

You can test for it yourself with a kit and paint right over it no problem.

I want it to be multi-family but I'm prepared to transition to what the market has to offer.

Are you prepared to manage all of those units for Airbnb and all of the different changeovers on your own or pay? 

If you choose to go on a month-to-month basis I would say be prepared to do that for a long time as they may scrutinize you.