I used Solus for years, it was actually my first long time Linux distro, and I have fond memories from that time and deep appreciation of the project. Note that I say used, because I have moved on (to EndeavourOS and later NixOS).
The reason why I moved on is the same as why I would recommend against Solus: the project have lost a lot of its core contributors. At the time I left there were no package updates for quite some time (used to be weekly).
I am not quite sure Solus really got a future. There are talks about converging it with AerynOS, former SerpentOS, which is innovative but still experimental software built by the original team, i.e. those that left Solus in the first place. Though they are really proficient in making the software, I do not think they have the same skillset for securing longevity through contributions.
In the end you should not care too much what people think. You will get the popular options for the intersection of Lemmy and Linux users, but popular is not always good nor what is right for you. Just try stuff and be ready to move a little through rigorous backups, you do have backups?
Nice writeup and a fun read! Never thought I would encounter a fellow NixOS and FoundryVTT user in the wild, but I realize the Venn diagram of these kinds of users do have more overlap than I thought.
With regards to your point about Foundry needing more power than a cheap VPS: I have it working fine on an Oracle cloud free tier VPS (unfortunately not the ARM-cores). That being said, it does want a little more power.
I am not running it with NixOS though. I am renting a temporary space, so I do not own or want to do too much locally right now, and Oracle OCI was only sort of working with NixOS. I did manage to install it with nixos-infect, but think I messed up the SSH with my reverse proxy and had no way to fall back to a previous version, which begs the question how would you?
You linked to “NixOS friendly hosters”, do those give you access to boot options to recover from such a case? Since I did not have that option I determined the risk of failure too great for setting up NixOS on that particular VPS provider.
I also note that you use the nix-foundryvtt module and was wondering how your experience with it was. Does your sops define your login to the website such that it fetches the package automatically or do you have to manually install them?