Many states want you to have a real estate license in order to serve as a property manager for other people, so I would start with confirming your states requirements. If that is the case then factor in the cost of maintaining your license to determine if it really makes sense with the low volume of properties you mentioned.
I also work a day job and manage my own properties, but I also have help. So I would look at friends and family that you trust that you may be able to share some responsibility with. Maybe they field the calls and you handle marketing, financials, etc. In my case, my parents field the phone calls, and call the vendors, I run the financials, marketing, etc.
Finally the last thing I would consider based on your post is the capacity for my vendor list to keep up with an increased volume of work orders and your ability to follow up on the completed work. Do you have multiple vendors for plumbing, HVAC, etc? If so, vendor throughput may not be a concern.