A spreadsheet handles the accounting for four doors without trouble. What software sells you is the stuff around the accounting: online applications, tenant screening, rent collected by ACH so nobody hands you a check, and a maintenance request that leaves a written record with a date on it.
Rough pricing, and confirm it yourself because these companies change tiers often. The landlord-focused tools have a free tier and a paid tier that tends to land somewhere between $10 and $30 a month for a small portfolio. Heavier property management platforms price per unit, often a dollar or two per unit per month with a monthly minimum that makes them uneconomic under about 20 units. Screening reports usually run $35 to $60 and in most cases the applicant pays that as part of the application fee, though how much you may charge for an application is capped in some states.
On the screening point, you can't just buy someone's credit file. Consumer reporting rules require a permissible purpose and, in practice, a vetted account, which is why landlords go through a screening provider or have the applicant authorize the pull through a platform.
Full-service management on a small building generally quotes 8 to 10 percent of collected rent, plus a leasing fee that often runs half a month to a full month of rent per placement. On four doors that leasing fee is the number that surprises people, because turnover is what you're really paying for.
One more thing: open a separate bank account for the building on day one. Deposit handling rules in many states require tenant security deposits to be held separately, and untangling commingled money later is miserable.
