How many devices can connect to a EX7700

I have around 40 devices, including cameras, thermostats, temperature sensors, five Amazon Echo devices, two cell phones, irrigation system, seven TV's, satellite receiver, five computers and four printers all yelling for attention. Most of the time it all works well but increasingly devices fall off line.

My one router is a Nighthawk X6.

Would adding the EX7700 make my system more reliable?

(I listed the EX7500 in the "Model" box above as a placeholder. The box is required but doesn't have an EX7700 in its catalog.)