Use CAT5E or CAT6A and buy some keystone jacks for easy installation. For the switch, buy a unmanaged Gigabit switch with at least 2 more ports then you need for future proofing.

Modems MODulate and DEModulate.

If it has Wifi, it’s not a modem but a modem/router combo(AKA gateway). What model is it and the router your thinking of?

What do you have as a router now? Sure you need a router and not a Access Point? Those are cheaper.

The levels look good although you are missing some downstream and upstream channels. Should be 32x4 at least. Do the signal levels change when you move the modem? Also, what part are you moving? Sounds like a broken coaxial port on the modem to me or something like that.

Signal levels?

Run Pingplotter to show where the latency is occuring. Also, test on wired connection.

ISP usually charge for extra IPs as IP addresses are limited. Wouldn’t affect your data/speed though. If you want multiple IPs look into business internet. For confirmation, who is the ISP?

Try from a wired/ethernet device.

Who is the ISP?

What model modem and router do you have?

What is the physical connection rate of the ethernet? 100Mbps or Gigabit? Also, what model modem and router do you have?

Have you checked your signal levels at 192.168.100.1? That might explain why 2 modems are “shitty”.