Well, the big challenges (rent control/stabilization, tenant friendly housing courts, tough renovations/need for expeditors, etc.) is NYC-wide, no differences between the boroughs there.As for Manhattan proper, my take is it comes down to two distinct reasons. 

Practically speaking,  these are 2 separate and distinct actions that most likely have to be undertaken.Much successBob 

But this kind of gets at my main distinction in the question compared to other posts I've read here about the topic...

The specific distinction is the HOA referring to my rental as a multi-family unit, which it is absolutely not.

How Home Staging Creates an Emotional ResponseEach home has a distinct ambiance.

I say this because many of us, myself included, have a hard time making that distinction.

Think if it this way...zoning and allowable use are similar but distinct layers of regulation.

It sounds like you want to:1) Lease the cottage,2) Have an option contract on the entire property, and3) Use seller financing when you exercise the option (see https://www.biggerpockets.com/...)These are three distinct steps, but each of them is fairly straightforward and just requires you and the seller to agree to terms and sign a contract (1.

I make the distinction because the bigger guys don't want the medium ones as they are more difficult to manage from afar because they don't support a dedicated on-site manager and handyman. 2.

The valuation and market value of a multi family property differs from a single family and you want someone that understands the distinctions.