It will likely depend on where you are looking. 

Depends on the city & airport. 

Also, you don’t need a business license just to look at properties, but if you buy a bigger property, like a multi-family unit, you might need a certificate of occupancy, depending on the local rules.For business trips, most expenses can be deductible, but if it’s part personal and part business, you can only deduct the business portion.

For these reasons i am confident you do not need an account per unit as having that requirement would be crazy complicated (the opposite if kiss).in addition, how will anyone know that you are not following the law?  

Depending on your goals and how you are buying your properties you may notice that certain areas are difficult to cash flow in NH depending on your strategy and what type(s) of properties you are looking at. 

I mean this depends on where you are at financially.

Some lenders offer creative solutions, like a cross-collateralized loan, where they use your existing equity as security without refinancing the duplex.Another idea is partnering with private lenders or exploring a second-position mortgage, depending on your lender's terms.

Or, depending on the property you could go non-QM with like a DSCR loan and close in an LLC or partnership.

It all depends.

You'll get differing amounts and qualities of leads depending on the type of marketing, but also depending on who you're marketing to and where.