Purchase of owner occupied duplex advice

[Jordyn Matusevich]

hi all,

I'm new here and seeking some advice. My husband and I, both 33 without kids yet, have lived in a rental unit of a house with one other rental unit for the last 4 years. The owner has just put the house up for sale and we are considering purchasing the house to live in the other, larger unit upstairs and rent out the unit we currently live in, managing it ourselves. The house is for sale for $320,000. We've paid $1230 for rent since we moved in so we think that it could rent for higher especially with some upgrades and repairs. The other unit rents for $1300 but has a lot more space (extra half bath and extra bedroom). I think the owner could've gotten more.  

We haven't met with our realtor or mortgage broker about it yet but if we put $25k down and got a conventional loan of $295k our payment would be roughly 1800/month (using a mortgage calculator). This would be over 5% down which is what we've been told we would need. 

Thinking with the 50% rule (I learned about here today) and we rented the unit for 1300, we would basically be able to pay our new mortgage with the added income for about what we currently pay for rent now, while upgrading to the bigger unit. $1300/2=$650. Payment of $1800-650=$1150, which is $80 less than what we pay for rent now. 

Does this sound correct? What am I missing? Taxes are about $4500/year but I assume we'd be able to depreciate half and that isn't reflected in the mortgage calculator so maybe we'd be making more. 

We are in a popular area of Philadelphia that inhabits mostly young professionals and college students so there are a ton of renters. Eventually we would plan to move and rent out both units. 

I appreciate any advice or help as to what else I need in my calculations and if this sounds like a good plan. 

Thank you in advance!

Jordyn