You need to find out what you meter size is and the line size coming out of the meter. Ideally your POC would be as close to the meter as possible.
Also you need to test flow and pressure at different times of the day .... the most important time would be during the normal run time of the irrigation system (ex. 3 AM - 9 AM).
Also curious how you are determining your dynamic PSI and flow rate?
Using MPRotators will allow you to put more heads per zone as their flow rates are relatively low.
I can't speak on what they appropriate mainline size should be. It depends on pressure, maximum flow and length of the line. Use the charts to determine what is the best size to use.