Minimal pruned bitcoind is OK. 12GB of storage currently required.

LN Gateway is not trusted and can provided by anyone. I envision that eventually there will be services that provide LN gateway to private Federations for routing fees, after some liquidity is provided. So Federation guardians just register for that service, give it some ecash to have in-Federation liquidity and that's it.

Unclear what you mean. The guardians don't need anything else. Users need something like a Fedi or Mutiny app.

The general process is hopefully well described in e.g. instruction: https://github.com/fedimint/nixos-deployment

Eventually it should become even simpler.

Guardians are the users themselves. That's how I think about it. You don't use random federations, or even reputable public federations, at least with any non-trivial amounts. You use a federation that you ideally run in part by yourself with other people you know and trust personally , along with your extended family, friends and close knitted community.