For the MAC address, you can use access control to block or allow access to your network. An Access Control List (ACL) works with the MAC addresses of wired and WiFi devices that can access your entire network or are blocked from accessing your entire network. If the user has something else in mind, please ask for more detailed information

Yes, by default the router works as a DHCP server. The router assigns IP, DNS and default gateway addresses to all devices connected to the local network. The default gateway address assigned is the router's LAN address. You can use another device on your network as a DHCP server or manually specify the network settings for all your computers.