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.

Now leased to market, under 4% vacancy/bad debt, and RUBS implementation.

Even if there isn't a lease in place, underwriting can use market rents from an appraisal to qualify.

My first tenants were paying ~1,600/month and current leases are climbing towards $3,000 a unit.

One lease for the entire house.

Consider auto loans, inventory, commercial paper, annuities and even RE and equipment leases.

Study landlord basics, especially on what to include in your lease (going forward you will ALWAYS have a written lease).(2.5 Learn from mistakes and don't repeat them.)

Also having a higher proportion of revenue generated through the residential component of the building does make financing easier. (3) The exception to the 80% rule I abide by is when the commercial space is leased to a credit tenant with a proven & sustainable business  or where the space presents the opportunity to attract a neighborhood amenity F&B operator (this is most beneficial in instances where you have a larger localized portfolio where these commercial tenants can positively impact the value of your overall residential portfolio).

I have been doing the property management and leasing myself, while sometimes trying to handle maintenance.   

I am pretty experienced with S8 procedures, all of that experience is with our Toledo LMH team.Are you leasing with a property manager in town?