Is there a limit to the number of low-power firmware devices that can access the wired Zigbee gateway?

Yes, only 32 low-power firmware devices can be accessed. If want to add more than 32 devices, you need to add high-power device as relay routes before you can add low-power devices. Each additional high-power device can add about 20 low-power devices, and so on, until the maximum number of gateways is added.