No, that's not enough. Especially not when a building control system is involved. The Fritzbox quickly gets overwhelmed with many WLAN devices, and a repeater is by far the worst solution to extend a WLAN.
If you have no demands on the network and just occasionally visit the internet with a laptop/smartphone/tablet, that’s probably sufficient. 1-2 Netflix clients also work. Beyond that, or with somewhat more intensive usage in terms of devices, number, and traffic, a Fritzbox will also reach its limits.