Which wireless communication solution is right for my needs?
I run a system using 2.4GHz WiFi where the remotes (clients, not APs) are ESP8266 so no limit as per @dandavis, the base station(s) are OPi 1 (wired Ethernet) and the wireless base station is a router which I already had in place for internet connectivity.  Central unit(s) schedule/polls remotes (using http protocol) so allows for bases:peripherals N:M.  Its not MCU to MCU, but the central unit is $12 delivered which is actually cheaper than most other wireless solutions I examined.  100m might be a challenge depending on your router and antenna arrangement, but 50m is easily achievable.