Check your state laws or local apartment association to confirm the mandatory on site manager issue.
For example, In California, if there are 16 units or more a designated ‘responsible person’ is required to live on site. As the number of units increase so does the staffing requirements. In addition, the resident manager is an employee (not an independent contractor) and therefore must be paid to meet local minimum wage laws.
If you are going to start with commerical (>4 units), I recommend networking with commerical lenders and showing them marketing brochures of properties you are interested in to see how much they could lend on any given property and make your offer subject to obtaining that amount of financing and interest rate you can live with. Most commercial lenders look to the cash generating abilities of the property first but may be more conservative if they feel you have limited experience in commercial real estate management.
If I was a newbie, I’d consider continuing with the current PM since they know the property. During the due diligence period, I am sure the current PM will be very interested in showing you why they should keep them and you should take the opportunity to talk to them about their practices as much as you can. If you decide not to use them, make sure you have gotten all the documentation and information you need before closing the purchase. If you decide to go with another PM, you will not get any co-operation from the previous PM after the sale closes.