I think that one of the below pump performance curves should go to your pump.
Once you are operational, you can plot your system curve on the pump curve to find the operating points.
The operating points are where the system curve intersects with a pump curve.
You can measure the TDH (Total Dynamic Head) or the flow in gpm and then put the dots and draw the curves as shown in a hypothetical example below.
If we assume 12 feet for the suction at 80 gpm, the pressure side should be the filter pressure x 2.31.
I would estimate the suction head loss to be about 40% of the return head loss.
If the return head loss is 30 feet, we can estimate the suction head loss to be 12 feet.
For example, if the speed is 2,750 rpm and the filter pressure is 13 psi, we can estimate the return head loss as 13 x 2.31 = 30 feet and the TDH would be 30 + 12 = 42 feet.
So, we put a dot at 42 feet on the 2,750 curve, which is 80 gpm.
Or, you can measure the flow and then put the dot at 80 gpm to find the head loss.
You can install a vacuum gauge to get the actual suction head loss if you want to be more accurate than estimating at 40% of the return head loss.
You can install a flow meter to see what the flow is to make sure that the flow to the heater is correct before you set the pressure switch or install a flow switch.
I would install a flow switch for the heater and a flow meter on the system and maybe add a vacuum gauge to the suction.
Notice that the pump will drop the rpm at 115 volts if necessary to keep the amperage below the maximum specified in the manual.
So, be sure to use 230 volts and not 115 volts.
The maximum is 16 amps at 115 volts so that the pump won't exceed 80% on a 20 amp breaker.