How to know if multi family unit is a good choice for first house

[Ronald L Gatewood]

I was looking for a house, but came across a fourrplex being advertised at $109,000. They are town house style apartments with 2bdrooms and 1.5 bath. I will live in one of them and get FHA loan.

Is there a formula or rule of thumb I need to follow to make sure it’s a good purchase based on the monthly payment I’ll be paying out for mortgage, insurance, & taxes. Estimated rent for the units is between $400 - $525.