I’ve been self hosting for 2 or 3 years and haven’t been hacked, though I fully expect it to happen eventually(especially if I start posting my blog in places). I’d suggest self hosting a VPN to get into your home network and not making your apps accessible via the internet unless 100% necessary. I also use docker containers to minimize the apps access to my full system. Best of luck!

I’m not aware of a new interface. Did it just change or something?

I use the Nextcloud News app. It’s not as fully featured as others, but it does the job for me. Just requires a lot of setup and has a lot of extra stuff with it if you don’t want to actually use all the Nextcloud features.

Learn docker. That should probably be #1. That will open up a world of self hosting options.

That depends. How new are you? What do you already know?

Not sure about the rest of those, but Obsidian isn’t OS either.