To summarize, our advice is do not “Loop”.
Run each skimmer line all the way back to the pump and put a separate valve on each skimmer.
Use a minimum of 2” PVC.
Keep the water velocity below 6 ft/sec on the suction and below 8 ft/sec on the pressure side.
Size.......6 ft/sec......8 ft/sec.
1.5"...........38...............51 gpm
2"..............63...............84 gpm
2.5............90.............119 gpm
3.0".........138.............184 gpm
Skimmers should not have more than 60 gpm at any time. So, 2” PVC is fine up to 80 feet. Above 80 feet, go to 2.5” PVC.
Also, do not get a single speed pump. Get a variable speed pump.
Can you provide more details about the entire pool and equipment?