I'm using nebula to remotely access the raspberry pi in my home network and it mostly just works. The dual setup for nextcloud might be a bit more tricky, at least if you want to use HTTPS. You'll probably have to set up a reverse proxy in Nginx for at least one of the routes, since they need different certificates (although since Nebula already authenticates and encrypts your traffic, HTTPS is probably not necessary there).

The problem seems to be that home.stateVersion is not set because you commented out both the declaration in flake.nix as well as the line that imports home.nix. It's a bit difficult to see whether the config is otherwise fine since there is a lot of visual clutter due to all the commented-out lines.

First, you need to pass the plasma-manager input to your home-manager config in some way. I use the NixOS module for home-manager which I declare like this in my flake.nix (if you have a different setup, this might not be necessary or you have to do it in a slightly different way):

homeManagerModule = {
  imports = [home-manager.nixosModules.home-manager];
  home-manager.users.myusername = import ./home.nix;
  # This will give us access to the inputs in the home-manager config
  home-manager.extraSpecialArgs = {inherit inputs};
};

Now the home-manager config (in my case home.nix) can look like this:

{
  inputs,
  ...
}: {
  imports = [inputs.plasma-manager.homeManagerModules.plasma-manager];
  programs.plasma = {
    enable = true;
    # ...
}

You probably forgot to import the plasma-manager module into home-manager. If you want to have a cleaner setup, I'd also recommend against just copying the complete output of rc2nix into your config since it tends to contain a lot of unnecessary stuff. What I usually do is:

1. Store the current config in a file, i.e. rc2nix > old-config.nix
2. Make whatever changes I want in Plasma in the graphical settings app
3. Store the updated config in a new file, i.e. rc2nix > new-config.nix
4. Get the difference, i.e. diff old-config.nix new-config.nix and add what I want to my actual plasma-manager config.

This of course only works if you're starting from a relatively unmodified installation of KDE, but in that case it's worth the effort imo.

That can be a good solution at least if electricity costs are not a big deal. If power is expensive in your area, it might be worth to buy something more power-efficient, like a raspberry pi (assuming they're not completely sold out right now).

From Wikipedia:

Fascism is a far-right, authoritarian, ultranationalist political ideology and movement, characterized by a dictatorial leader, centralized autocracy, militarism, forcible suppression of opposition, belief in a natural social hierarchy, subordination of individual interests for the perceived good of the nation and race, and strong regimentation of society and the economy.

The only part that could vaguely be associated with capitalism (in a democratic country) is "militarism" and even then this is only the case if you mainly focus on the USA. The fact that fascist countries were running free-market economy is also not really a point since that was (and is) the case for a large part of the world.

"subordination of personal interest" and "strong regimentation of [...] the economy" is the opposite of prototypical uncontrolled capitalism. Saying that capitalism is fascism is just as stupid as saying that fascism and socialism are the same ("bUT it wAs cALLed naTIOnaL soCiaLIsm"). Using the word "fascism" for everything you don't like just makes it lose all meaning.

I think this should work assuming that the game and mods are compatible with proton. Also, you don't need an external drive, you can access the windows partition from linux (probably not the other way around though since linux understands NTFS but windows doesn't understand ext4). If there are any issues, maybe try the "Verify Game Files" feature of steam. This might remove the mods but at least you don't have to download the game again.