I have a cheap Bluetooth controller that works perfectly for me, although to be fair I almost never use a controller so it gets used a couple hours in a month lol. The brand is gamesir and I got it for $20 or so with no issues on Linux using either the Bluetooth mode or the 2.4GHz adapter over the past couple years
Honestly case-wise you just want something you like the look of that fits all your stuff and has some ventilation lol. In your case that’s just checking that it fits an ATX motherboard, the height of your cooler, and the length of your gpu. For your cooler and gpu most mid tower ATX cases will probably fit no problem, so try to narrow things down based on looks/style and having a couple fans (or at least room for them) first and just check dimensions once you’re seriously considering an option. A case that comes with fans is usually cheaper than buying fans separately so that can be a plus for cost savings, but if you’re picky about noise or airflow choosing your own fans lets you optimize for either/both. Different cases will have better or worse cable management options, but if you’re the type to build once for a while and not swap cases or motherboards all the time you may not care too much.
Basically:
Looks like a great build, only two recommendations personally:
first, make sure the ram you get is 6000MHz, and in the case of Corsair vengeance they have a CL30 kit and a CL36 for prices that usually aren’t too far apart. If it’s close in price CL30 is better, but if not CL36 isn’t awful (or you could pick up some equivalent CL30 ram for cheaper from gskill or teamgroup).
also someone else already mentioned the SN850X, which would be a great upgrade (2GB/s faster read speeds) but depending on pricing the new sn7100 might be a good middle ground.
Otherwise assuming you slap a decent cooler on there the build looks perfect to me, and the only alternative I’d mention is just that cheaper and similar looking cases exist if you want to cut costs a little to make up for spending more on the ssd (deepcool’s matrexx comes in a mesh version with a similar look to the 4000d at usually half the price with four fans, ime). Have fun with the build!
Plain 9.1 surround works fine with pipewire, and you can pretty easily hack together a virtual surround for stereo headphones that works pretty great. I’m even using a preset that claims to be atmos, although that seems unlikely to me lol
Using spectacle and vencord (or element for matrix) works fine for me on plasma, although element has a much lower bitrate sadly
Not an ultrawide or multi-monitor user (single 4K 27” miniLED for me), but hdr support is so close to being perfect but not quite there yet. The support has finally been added to Wayland git and is coming in the next update iirc, but at the moment it relies on your window manager’s implementation (KDE’s works great) and doesn’t work for gaming without running gamescope (steam’s window manager) in a window. The only issue I think will remain with HDR after the next update is with apps that stubbornly use X instead of Wayland (steam is the one that kills me here), since X won’t ever support it so those apps will be SDR.
In terms of OLED support, they don’t need to be treated specially to work so any of them should work as normal - only thing to be aware of is that WOLED panels made by LG (used in asus monitors too) use an uncommon subpixel layout and you may have to set it manually or fiddle with your text rendering settings a little to see it perfectly. Samsung panels (like the ones Alienware uses) use the normal layout so no concerns if you go with that. Otherwise, screen dimming / turning off after a period of inactivity is a common feature and should be good enough for protecting from burn in. The only other OS-level feature I’ve seen related to OLEDs is shifting sustained bright pixels around to share the load - not sure if anyone’s made this on Linux, it sounds awful to use so I’ve never looked into it.
Someone else already mentioned old games not supporting ultrawide well, but worth adding if you go OLED you can just run it 16:9 and the letterboxing won’t be nearly as obnoxious as on a standard IPS/VA/TN/whatever monitor that would be blasting ugly blue/black light from the “disabled” areas.