For the Wi-Fi Access Point (or router), we utilise the existing standards.
The CTC modules all operate only in the 2.4 GHz band. Nevertheless, a router with an additional 5 GHz is worthwhile. Because if you connect your tablet or smartphone to the router via 5 GHz, you ensure that the communication is enforced via the router, which often has a better wireless connection to the CTC module.
We have had good experiences with the FritzBox 4040, which we currently use for the CTC-Router. But an older (used) Fritzbox will do just as well. However, these usually boot noticeably more sluggishly.
Experiments with RaspberryPI with OpenWRT have not satisfied us and are hardly cheaper than the FritzBox 4040.
Experiments with FritzBox 7170 have shown that this unit gets tangled in UDP communication after uploading config files. The status of the modules turned to red. Only disconnecting the PC from the model railway Wi-Fi and reconnecting it brought the system back to life. With a (newer) FritzBox 3272, however, this problem did not occur.