Niri is a joy! Tried it once and never looked back.
Nix is a wide ecosystem and you have tons of tools to use for your config to your hearts content, so this is a bit tough. Id say: Make your config a flake (its an experimental feature, but it’s a de-facto default), use home manager or GNU stow to organize your .config and home directory, and if you like Nix and plan to stay, look into the dendritic pattern for your config (not the best for someone just testing nix, but for long term it’s a total life-saver)
Best of luck to you!
Yup it is. You configure your whole system by setting options in your config files, using a functional language. It’s hard at first but with time you naturally get used to it