Phoronix article: https://www.phoronix.com/news/Steam-Machines-Frame-2026
Also listed here: https://store.steampowered.com/sale/hardware
Valve has already sent support for the new Steam Controller upstream: https://www.phoronix.com/news/New-Steam-Controller-SDL
I think a wired connection is the key, one of my house projects this winter is running Ethernet through the attic finally
Having both on a different connection is essential!
If you have a spare router, you could connect it via ethernet to the host and then connect your client to that WiFi.
Host would then be able to maintain its internet connection over WiFi and there would be a separate dedicated LAN just for the stream.