Sancable 4 Port Cat6 Ethernet Female to Female Decorative Wall Plate in White

Will these have any issue with PoE?

can I mount this into a 2 gang box and use a double decora plate?

Would I just wire a cat6 cable regularly and attach a male rj45 jack to it then plug it into the back of these connectors?

Can I get a combination of cat6 and coax?