Renting a multi-family 2nd home for part of the year

[Darrick Lowe]

Property Owner in New York. I'm looking to purchase my first multi family home. Looking at 2-family homes, where I rent one unit out and have the 2nd unit be my second home. 

When getting a mortgage, should I tell my broker that the property will be my primary residence or 2nd home (or a rental)?

In addition, if i rent the 2nd unit for part of the year (on airbnb for example), is that ok from a lenders perspective? I assume if I rent it out for 300 days out of the year that would be bad, but what if I rented it out for 30 days out of the year? Is there a threshold? 

Are there any specific income tax considerations I should look into for the 2nd unit? I know that renting for 14 days is tax free.

Thanks in advance for the help!