As easy as downloading an app from the store and telling it which directory to work with.

If you need the AI features those require separate apps and depending on your deployment it might need some effort. I'm running a docker image and had to ensure I have some of the required libraries for the AI things to work. It isn't too hard to misconfigure though and I believe there's a decent amount of resources for this.

As for mobile app, there isn't an explicit one but the webapp interface is mobile friendly and works pretty well. I also use NC photos and it still works with the tags and face recognition things. That app doesn't require "Memories" as far as I know.