I normally say 100Mbps per person. That is enough speed to stream around 4, 4K Netflix streams at once. Or 1 stream and browsing the web and other things at once.
If there are 2 people living there, then 200Mbps. Normally you’d have to go with a 300Mbps plan. Which is more than fast enough for most people.
My Brother and his wife life on top of a mountain basically, and have wireless Internet, and get around 100Mbps. Yet that is enough speed for the both of them to work at home and be on their computers.
If most of your bandwidth is being wasted, why have it? Now there can be reasons why you need more speed. If you do a lot of Peer to Peer and want to transfer a whole lot of large files all the time. Faster speed, won’t take as long as slower speed. Will it make it worth it for you? I doubt it.
All your devices don’t need 50-100Mbps non-stop. They grab a batch of packets and then stop. While some other device is grabbing some packets and then stopping. While other devices aren’t doing anything on the internet.
If you’re doing a lot of waiting around for something to happen on your devices because you’re using so much data, then yes, you need more speed.
I normally recommend 2 runs per location minimum. If one fails for whatever reason, like a mouse chewing on a cable, you have a backup.
Running Ethernet to my garage was a big plus also!!! I would like to run Ethernet out for a Doorbell, but that isn’t going to be easy with my house. Ethernet for Smart Doorbells is a growing thing.
PoE Security cameras. You might want some in the future. Running Ethernet for that NOW would be easier than later. You leave a bundle of wire at each area you thing you need a camera and it all goes down the the basement.
How about Speaker wires for a surround sound setup? Maybe Whole Home audio? These are some things to think about with new construction. Ethernet for TV Locations!!! Wired is always better then Wifi.
With your Modem downstairs, how about Wifi Access Points mounted on your ceiling? So you can have great Wifi everywhere you go. This would really help if you want to get into some smart home stuff.