For a media server :

• Audiobookshelf for audiobooks and podcasts (for podcasts it can fetch them online from a RSS link and download them, you don't need to manually download them)
• Jellyfin for films, series and music (for music you can use jellyfin as backend and another app as frontend if you don't like jellyfin's music player, a lot of people find it lacking)
• Komga for reading comics and manga (there's also Kavita but I haven't tried it)
• Komf for fetching metadata for comics with Komga or Kavita
• Suwayomi Server for manga (it doesn't only act as a reader, with extensions it can find manga online and download them; it can sync your reading progress with AniList, and it's compatible with Tachiyomi if you need that)
• Haven't found one yet for ebooks. I passionately hate Calibre and wouldn't touch it again with a 10 foot pole, but a lot of people swear by it so you might give it a try and see whether you love it or hate it (it's usually one of the two). Be warned though, it will automatically rename all your books and sort them in subfolders in a very stupid way, making it difficult to find anything again manually. So if you want to test it, do it on a copy of your ebooks first, that way if you don't like it you won't be stuck with everything in your ebook library renamed weirdly (speaking from experience -_-).

Cloud :

• Nextcloud : your very own locally hosted Cloud.

Everything can be run in docker containers so your distro or even OS doesn't matter.

Hardware :

• Personally I run everything from my NAS in docker containers but it's starting to get overloaded so I'm planning to make a dedicated media server on a cheap mini PC like a refurbished Dell OptiPlex SFF.
• You could also go for something like an OrangePi or RaspberryPi if you don't mind using ARM.