If you don’t mind a dongle on the USB-C port, Soundcore VR P10. It uses the LC3 codec between the dongle and earbuds. I’m usually sensitive to latency but with these it’s at a comfortable level where I can game with them properly. The dongle does have passthrough charging but the Deck will not be able to fast charge with it.
I would’ve thought the Ryzen 5 would still do a decent job, especially as it’s 7000 series. Not sure the 1335U will be an upgrade at all, more likely a side step. If anything it seems more like the lack of a stronger discrete GPU is what’s holding you back, based on other comments of the software requirements.
Depending on the dock you’re using 1440p at even 120Hz works. I’ve even done dual 1440p but had to drop the refresh rate to 60Hz on both. Haven’t had any issues with this setup.
Depends if you have a reason to install Windows. If you’re mostly playing games, especially from Steam, you’re fine with SteamOS. If there’s some games you do play that don’t work under SteamOS (eg developer refusing to get their anti cheat Linux compatible, game pass, etc.) then go ahead with Windows. Personally I dual boot both OSes, Windows is only used for those anti cheat games but I much prefer SteamOS for everything else as it feels more comfortable to use on the Deck.