So you'll have to really think how badly you want to try to save these, and where they're going. 

Here are some things to consider:Most investors don't need software until they have 5-10 rentals.

There is no differential factor number, however, it will change if you are buying tenant occupied, if they are are going to be vacant at closing, if they are going to stay the full lease or you have to pay cash for keys.

They send money to title company at closing.

This all seems very subjective to me.

Welcome to BP! 

I've currently got 2 multifamily properties here with 5 total units -- I live in 1 of them.It's been extremely difficult to find multifamily properties that meet the criteria that I'm looking for through the MLS, and when I do, they're extremely overpriced.

and want to build new a larger house to accommodate.

After doing some initial research, I decided to check out some zip codes in Philly as that's an hour's drive from where I live - 19132, 19133, 19134.

Check out the exceptions to the law as it does not apply to all rentals:https://www.nyc.gov/site/hpd/services-and-information/good-c...If it did apply to you, month-to-month agreements would still allow you to do rent increases any time.