And if you do not think you will get caught, a lot of nosey neighbors will call you out on it (we did not rent a basement but we had built a shed as an outdoor dog house that was heated and air conditioned and someone called about that on us...).

When I had a duplex I just put up a second box with a "B" on it by the entry to the second unit.

@Dennis Boettjer be careful about basing your decision solely on past deal performance.

I am currently going through the process of closing on my first multifamily deal.

Focusing on both flips and buy-and-hold multifamily properties in NH sounds like a solid strategy and great market to do so in.

looking to rehab on a property soon

I typically build in an inspection contingency into my offers (yes this reduces my competitiveness of my offers, but its also a safety net to protect my bottom line).

Here's an article with additional FAQs on cost segregation studies.https://www.biggerpockets.com/forums/51/topics/1113749-cost-segregation-faq

I'm still having to run the numbers on each project and see what makes sense.

If you are buying a high cost property with litle to no cash flow, you likely don't have to worry about paying tax on rental income since your depreication will wipe out any cash flow from being taxed.