I pay $50/mo for 1Gbs here in TN. How low can you actually go on the price? Typically you don’t see anything less than $50/mo for Internet that not exceptionally bad. I’d keep the 1Gbs. Most routers these days are capable of 1Gbs unless QoS is needed at that speed too.

For switches, it’s pretty much a commodity item. I prefer Trendnet at home because they actually had a simulator on their website showing the GUI. For more professional gear, I’d use FS switches. For AP’s, I use Grandstream.

There’s no issue with using MoCA. There’s also G.hn which achieves the same thing via unused coax. The advantage of G.hn is that it doesn’t require special splitters to accomodate the frequency range; the disadvantage is that it conflicts with the TV frequency range which is why it needs to be unused coax.

https://www.amazon.com/dp/B09SKSKQR3

Your house is too large for adequate coverage by a single device unless it has no interior walls and you don’t care about the speeds as you get further from the wireless router.

You should be looking for a router without WiFi but with proper QoS. Your WiFi can then be done with multiple AP’s to provide better coverage throughout the house. You just need cables from your switch to the locations where you’d want to put the AP’s. The solution to bad WiFi is not a more powerful transmitter. You need to reduce the distance to each WiFi source which you do by adding more AP’s. In a case where you can absolute not run cables and nothing currently exists for MoCA then you would use mesh but it’ll never be as good as a cabled solution.

If you want coverage to the detached workshop, run a cable there and add an AP. If you can’t run the cable then use a wireless bridge designed for point to point and then add an AP to that.

You could actually expect less than 20Mbs because of congestion issues assuming no QoS and you’re right that any port might get more at any particular moment of time. This is mean to be an illustration of bottlenecks and not an implication of layer-2 load balancing. The traffic just can’t be more than what the bottleneck will allow.

Link speed is your hard limit – you can’t go faster than that. Nothing gets divided up just because a device is on. The concept of bottlenecks is what’s important. If you had a 100Mbs switch (with 1Gbs uplink) and a 1Gbs router with a 500Mbs ISP speed, a PC on the switch will be bottlenecked at your 100mbs switch port – it won’t be able to go beyond 100mbs. If you have 5 PC’s on that 100Mbs switch all trying to do 100Mbs each (since that’s the bottleneck of the switch), each PC will be able to do 100Mbs and since you have a 500Mbs speed connection – each PC should get 100Mbs. The switch uplink will pass 500Mbs/1000Mbs and the router will pass 500Mbs to the ISP. If you add a 6th PC trying to do 100Mbs then it gets bottlenecked at the ISP link since it can only do 500Mbs even though the router can do 1Gbs.

If your 100Mbs switch had no 1Gbs uplink then the fastest switchport to the router would be 100Mbs. In the first scenario of 5 PC’s trying to do 100Mbs each, they would all be throttled to roughly 20Mbs since the total connection out of the switch would be 100Mbs. If only 1 device tried downloading, the limit would be 100Mbs for that device since the limit would be the link speed of the switch to the router.

If you had a PC directly connected to your router at 1Gbs bypassing any 100Mbs switch limits, the bottleneck would be at the ISP of 500Mbs. If you had devices on the 100Mbs switch (with 100Mbs uplink) trying to download at max capacity while your PC was directly connected, your expected speed would be 400Mbs since 100Mbs would be going to the switch.

The concept of a 24-port Gigabit switch with only 1Gbs uplink works because no device is expected to be constantly utilizing 1Gbs for a sustained period of time. They also supply full bandwidth to ports across the switch that don’t have to go across a common uplink. PC A and PC B can talk to each other at 1Gbs if on the same switch while PC C is talking to the Internet at 1Gbs. As long as the devices aren’t utilizing a common port at the same time, there’s no bottleneck.

You should be concerned because this isn’t normal based on the number of people, the devices, and what you are using them for. The first thing that I would look at would be Windows to make sure you’re not acting as a peer to peer client for updates – make sure this feature is turned off.