Each one of these things is a separate topic/project. There is of course, overlap, but concentrate on just one at a time. If you try to do everything, you'll go mad. Application Administrator, Network Engineer, Sysadmin, Network Security, are often separate full time jobs. Just concentrate on your own needs, one at a time, then focus on how simple you can pare down that one thing you need/want to self host. What is the minimum set of capabilities you must have for this one thing? Then, expect to have as much research for this one thing as taking a 1 credit college course, at least. Maybe more, maybe less, depending what it is. That's a more realistic set of expectations.

I've done a lot of web design and web hosting, and messing with Linux server stacks for around 30 years, now. You absorb a LOT over time, but it is all always changing. When I set up my first server, Cloudflare didn't exist yet. VPNs weren't a thing yet. The only people I knew with a network in their home were Computer Science professors. Wifi was not a thing yet. It isn't you being inadequate, it's you trying to do multiple jobs that each require constant professional development.