And the are all managed professionally.

Hi @Curtis Osawey Welcome to the REI world!!!

I am patient and can wait for the right deal to come along. 

When it comes to rude and abusive tenants, I'll deal with them on a professional level during their tenancy, but when it comes to renew, BYE BYE.

What you can require legally changes depending on your location. - If you make the above clear in the listing, you will immediately get fewer applicants.

What can be the disadvantage to keep it aggregated in the coming years?

Assuming you currently rent right now, and you are buying the single SFR as a primary, the 3-unit should just be designated as investment and you should be able to use the rents to offset the payment (up to basically 'zero-ing' it out, on paper). 

Here is a video that runs down the basics - https://s-media.nyc.gov/agencies/specialenforcement/01-Legal...There is also a prohibited building list - https://www.nyc.gov/site/specialenforcement/registration-law...Here are some more info overall - https://www.nyc.gov/site/specialenforcement/registration-law..All of this makes STRs in the city pretty tough but it certainly not impossible.

When it comes to housing, the FHA rules apply in addition to those of your state/city.

Post the notice as soon as they violate the lease and it should come from a lawyer not you.