This is a major hole in your setup.
Proton Unlimited gives you a premium SL membership.
If you create a linked account and you’re subscribed to a Proton Unlimited, Proton for Business, Proton Family, or Proton Visionary (legacy) plan, you’ll receive SimpleLogin Premium for free.
This is an odd one and I am not 100% sure of my answer but my understanding is if you create your aliases via SL those aliases are permanent (ie even if you lose your SL premium membership, the ones you already created will stay there).
If you create the aliases via Proton (ie through pass) I think you are limited in what is kept per your previous thread