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.
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!