Nvidia GPUs seem pretty solid with the latest driver developments around Wayland explicit sync now. I haven’t had the experience with a modern AMD GPU to compare, so hopefully others can chime in there. I think AMD stability depends on which driver you use.

As for AMD CPUs, I don’t think you can really go wrong if you go with the x6xx class or above. The X3D variants are supposed to have a bit of an edge in games but a very slight penalty in other general computing tasks. Doubtful it would be anything perceptible other than in benchmarks or compile times. If your system is primarily being built for gaming, I’d say opt for an X3D part if all other things are equal. If it’s more of a workstation kind of system, or you plan to leverage a lot of virtualization tech, I’d say spend as much as you’re willing to stuff as many CPU cores into that machine as you can.

As for memory, more is always better. I’ve got 32 GB on my main system and never felt like there was anything it couldn’t handle, and that’s even being somewhat sloppy leaving other fairly memory intensive programs running in the background while I game. In that department, I’d just go with 32 gigs and call it a day, unless you’re doing video capture/editing.

Nvidia Gsync shouldn’t be an issue in Linux, at least not with an Nvidia card. If the monitor doesn’t also support Freesync, then that might cause a hassle with an AMD card.

Good luck and have fun!

Can’t speak to all of your points, but the main thing I’d recommend is to try distro hopping with some of the common recommendations. If you have a spare drive that would be the easiest. Mint and PopOS are probably the first two worth trying to see how things go.

In terms of games, you should really be checking protondb for compatibility. It shows the C&C series generally looking pretty good. If you’re out of the loop, Proton is essentially an improved version of Wine that Valve maintains that’s focused on games, but it’s free for anyone to use.

For text editors, there are an insane number of options. I’ve been pretty impressed with Kate from the KDE folks. Ties in best with a KDE-based flavor of Linux, but works great everywhere. Codium is a fork of VSCode that strips out all of Microsoft’s telemetry. Also great to use and very powerful with insane flexibility through plugins.

Regarding fragmentation across distros, you’re mainly looking at RPM-based (Fedora, Suse), deb-based (Debian, Ubuntu, and a whole slew of others based on those). Most programs will be bundled up as a deb or rpm. Efforts have been made to make more platform-neutral packages for distribution like Flatpaks, Snaps, and AppImages. Those have their quirks, and people have strong opinions about their merits and weaknesses, but generally you’ll be able to get those to work on any distro without much fuss. There are some cool utilities like Distrobox which do a pretty good job of setting up containers for different distros so you can install and run their native packages.

I’ve got an R3 at home which generally works well. Flashing mainline OpenWRT was pretty smooth and easy. It’s been a while since I did the bring up, but I do remember having to jump through some hoops to get a partition layout that would utilize the onboard storage properly. By default it only left 10mb to install additional packages which seemed to defeat the purpose of having all of that emmc available. That may have changed in the more recent releases.

One bug I encounter regularly is that some (maybe older?) Apple devices seem to be able to lock up the router. Adding watchcat can get the thing rebooted in less than a minute in the event that it does hang, which makes it barely noticeable, but it’s not an ideal fix.

Depending on the devices you have in your house that might be a showstopper or of no consequence at all. Otherwise WiFi speeds and signal are great, as are general performance and reliability except for that bug I mentioned. Haven’t used VLANs but it’s all there and the flexibility of OpenWRT is great.