I usually convert pdfs to epub if its something I actually need to read and not just scan/browse. Often I would bother to even edit the epub in Sigil to fix any problems with the conversion.

Network chuck has a really easy to digest series on how DNS and subnetting works, there are also free courses from free code camp on the topic, but those are less digestible.

Yeah, I just use the fork.

I just use Obsidian + Syncthing + MEGA. My obsidian folders are on my mega synced folder on my pc, and they are set up to use syncthing to push updates to all my other devices (2 phones and a tablet), but you can have as many devices as you want. It’s all free as well, and the cloud service can be any that you like.