Four unit building - keep at 4 or fix up unused 5th?

[Lora P.]

Hi. I have my first rental property under contract. There are 4 rented units. There is a 5th unused unit in the basement, and it looks as if it hasn't been used in a long, long time. Should I fix up the 5th unit and rent it out? It seems like that would be against zoning and screw up my financing, insurance, etc since it would make this property commercial rather than residential. Maybe it would be better to combine one of the units with the basement unit, to increase from 1 bedroom to 3 and keep the overall number of units at 4? Opinions?