Sounds like you have a pretty good grasp on your situation. Seems like you have around approximately $3,400 in P&I, Insurance, Taxes, and PMI if required with your loan. I don't know your market but how much could you get for your friend's bedroom and bathroom assuming he finds other living arrangements? If you get some similar to what your getting for the other one the house would be costing you $800 before other expenses like vacancy, maintenance, capex, and utilities. Not bad to have a cheaper place to live.
I think your plan to stay there for 2-5 five years is good if you save money to put towards future investments. I'm not sure if you're looking to buy properties in the same area you are currently in or if you will look out-of-state. Depending on appreciation you could have a decent amount of equity in the coming years. At that point you'd have to analyze exactly what you want, do you sell and buy a bigger home for you and your family, sell it to invest in better properties, keep it as rental, keep it as a rental and perhaps get a HELOC or Home Equity loan to invest in another property with the proceeds.
Hopefully this gives you some food for thought.