I’ve been doing some research on the property tax and haven’t been able to find a crystal clear answer other than the base 6%.

If RE is brand new to you, I would focus on playing defense:1.)

Our jobs base has been growing steadily and we're currently 12-13k rental units short of upcoming demand (based on published jobs coming to the market).  

I wonder if I could deduct mortgage interest based on the basement's proportion to the entire house (1,600/(1,600+2,000)).

Decide which game you want to play.

You’re playing it smart, darlin’!

@Emma Hustiswell, they're separate - you'd negotiate the price and terms with the seller, and now that's your mortgage payment (principal and interest, or P&I)then, you plug that mortgage payment in, as an expenseso, use a mortgage calculator first to generate the monthly payment, based on the seller financing termshope this helps

Based on your assessment of the spread, if it makes sense, then jump in and make an offer but try to push the settlement date back as far as possible to give you enough time to come up with a detailed execution plan for turning the property back into market. 

Usually you get a long term loan from a conventional lender like a DSCR loan that is based on the property income.

Of course site specific details could change my take above, but based on what you shared you need to buy a SFR in the two allowable areas above in order to obtain a STR permit.