The number of fans depends on the power draw of the fans. The EK Loop Connect can handle 20 W per fan header, so as long as the sum of the power of your fans on a single header doesn't exceed 20 W, everything should be fine.
If you are using the standard 120 mm EK Vardar fans with up to 2.16 W power draw, you should be able to connect up to 9 fans per header without issues. With the 140 mm Vardar EVO fans, up to 5 can be connected to a single header.
Anything with a higher power consumption just needs some calculation - Max. header power output (20 W) divided by the max rated fan power draw.