This is my personal daily work neovim config if you would like contribute be free to make a pr. Or you can copy this config.
I use this mode to test plugins that I'm working on. To run neovim with dev mode execute neovim as usually but the last argument must be dev.
$ nvim . dev
To set themes you'll need to set an environment variable named EDITOR_THEME.
Then neovim will load the theme and if it not exists will set the default theme.
EDITOR_THEME="nightfox"