I’m not sure I follow. You can terminate your cables into wall mounted sockets just like your electrics. What’s the issue with this?

No, because a switch can’t route traffic from one point to another. Specifically, it can’t do NAT. Without NAT you can only have 1 device connected to the internet.

Try connecting your computer directly with a cable 9t at least test your Internet speed right next to the router. Whatever the result is the best you’re going to get from your ISP.

It does, but it is also gradual over that length. Cat 5e cables are rated for full 1gbps at 100m, so in your case it’s not worth worrying about.

Yes, that’s very true. But worth remembering that while you can usually get away with cat 5 for 1gbps, that’s only up to a certain length, depending on the quality of the cable. If your cable is in or around the threshold for that particular cable where noise picks up, you could get inconsistent speeds like OP is.

Inappropriate cable?

It won’t be enough. The second you start watching a couple of netflix streams at 4k your connection is going to be nearly at capacity and unless you have some sort of effective qos on the router you’re going to suffer potentially from bufferbloat - increased latency which will make gaming agony

You contradict yourself on paragraphs 5 and 7. First you say it’s reachable from the outside then it isn’t.