It did take quite a while for Immich to process everything when I initially uploaded my library, how long has it been since the initial upload?

Kind of, you can share individual albums so it is possible to share all but one. This may or may not be practical though depending on your album structure.

Another option is to share your entire library but archive the photos you don’t want to be seen.

It would be good of there was an official feature for this but these are currently the two best options.

My only advice would be to go full NextCloud at first for simplicity instead of trying to integrate it with other services.

That being said, if later on you’re looking for a way to store images I’d highly recommend Immich, I just finished setting up my own hosting setup a few days ago and it is gorgeous.