MaM and Geek and some other sites post a weekly 0-Day dump from the comic usenet boards.
So every week, all the comics for the week a dropped in one bundle. “0-Day Week” is what they’re called.
Make an feed in your usenet/torrent/autobrr client to auto dl these weekly packs. Then in mylar add it to the folder-monitor.
To “quickly” (processing takes a while) jumpstart a collection go to MaM and download entire years worth of comics and have mylar import them all.
Please use MaM as having seeders is really important for all these comics.
I use tachiyomi with readcomiconline.li and readcomicsonline addon and I always get what I am searching for. I can download to read later and the ui is pretty good. Your solution sounds great but I don’t need all the comics in the world.