nix-dotfiles VS coc-metals

You can check mine out. There are also some here

You can also try my full config: https://github.com/mjlbach/nix-dotfiles/blob/master/nixpkgs/configs/neovim/init.lua

I do, in fact, use expandtab

Here's my init.lua. Neovim nightly will read this by default if you place it at $HOME/.local/share/nvim/init.lua. I use this configuration on the neovim source (c/lua) with clangd and sumneko language server, and on projects for research (python mostly), amongst other things.

Not yet! w is window and o is options. You can check out my init.lua for most of the common ones.

For autocompletion, I recommend completion.nvim. Here is the pertinent part of my init.lua (uncomment require'completion'.on_attach()), but you can wrap this in a lua heredoc if you're still using an init.vim.

Which server? Here is a minimal init.lua and my personal init.lua

You're not actually using any of those channels. You need to overlay the channels onto your package set. If you hop on the IRC or discord we can work through your specific error message, but here is how I have it configured (with home-manager):

https://github.com/mjlbach/nix-dotfiles/blob/5f956f9548bdf7f9c954c926e6ab24e94c4bf55d/nixpkgs/configs/neovim/init.lua#L380-L425

Hello Everyone! This Saturday the 10th at 3pm CEST I'll be doing a special livestream where I walk through setting up Metals to use with Vim and go over all the features. We'll look also look at the differences between coc-metals and nvim-metals. If you've ever been curious about Scala development in Vim, or just want to see Metals in another context, feel free to come hang out, lob questions at me, or just talk Metals and/or Vim.

From my experience with maintaining a coc plugin, coc-metals and also a new nvim lsp focused plugin, nvim-metals, I'd say in general, yea it has a ways to go yet before an average user feels it's as stable as coc is.