Books and comics I do grab manually, as I haven’t found something that works super well.

However, I have started using Kapowarr for comic management and mass renaming to match the file/folder structure Komga expects. It is still lacking some features but the developer has been making steady progress on it and the only two major features I feel its missing are metadata creation, and torrent indexers. The latter of which should be part of the next version and may boost its ability to automate downloads. I can’t attest to its manga support as I don’t read any, but it grabs its metadata from comicvine so that will likely be the determining factor. The developer also only permits LLM generated code under rather strict rules iirc.

As for ebooks, I grab them from my chosen source and just use the upload button in calibre web automated. I haven’t found an automation tool worth using yet, but I do like to keep an organized library in case I want to revisit something or share it with someone else.