New landlords dont know the dynamics and all tenants are different, Im not a fan of being neighbors even less roommates with your tenants.

Ive been living with roommates with monthly expenses down to 600-700 a month with every single bill i have.

:)  I am 40 now, but I bought my first home at 23 and lived in it with a couple of roommates. 

You could also if it’s two bedroom units in the fourplex get a roommate for one room and get a signed lease for that to increase your income.

I rented my house out to four roommates who all signed one lease.

Thankfully, our tenants made it through okay, transitioned to working from home and throughout this ordeal only one roommate within our portfolio got behind on rent.

Seems that a MIL suite would attract buyers looking for a space that they could either AirBnB/VRBO, house-hack (off the books, roommate-style), or put a genuine in-law into, depending on what stage of life your buyers are in.

You need quiet hours, you need to be respectful, you must quickly learn to screen tenants properly and thoroughly I do think sharing your home or apartment with a roommate is harder and not for everyone.

My second question then would be, does having a roommate who pays 400 a month count as rental history/income or is that different since I wasn't renting the entire property?

I rent the upper unit and have a roommate in my unit so I have no bills at all.Where are you looking to find properties?