Hi I have not yet purchase a modem and router because I cannot find anyone in a retail space to give some tech specs and websites also gloss over.

I need a device that can:

Mobile 3/4/5G
Whitelist websites (not blacklist only)

Block devices (MAC address allowed)

Connection to ideally 40-50 tablets

I believe a mobile modem as a gateway and connected to a router via Ethernet cable and use the router to give more control.