You mention using a Mac, so how about Photos? I store +300,000 photos/videos ~3TB in photos on a dedicated Mac mini (not using iCloud) with attached SSD and an external drive for backup. Works super fast, searches, filters, identifying faces, locations. Gave up the concept of folders once I was all in and its all by albums and search.

Been using Plex for years. Works great for me. Easy to setup. lots of clients.

What is your issue with exporting from Notes? Docs scanned are still PDFs and easily shareable/exportable with one click with Airdrop/email etc. And I find the indexing excellent, so I drop everything into Notes now and forget about it, and when I need something, a simple search pulls it right up.

iCloud mail is working great for me and it's totally free. Apple does the hosting, you'll need to own your own domain, and you can use one email address with it (not sure if here is a way around that).