As much as possible :) It's also the only app I really need direct access to when I unlock my phone.
Simple for me
Maybe try the Atomic version of Fedora Budgie? With my limited testing it looks like a really easy and (almost) unbreakable distro.
Otherwise uBlue has allot of images, you can make your own even.
Maybe try installing trough a package manager like Winget or Chocolatey
Well, uBlue can be as light as you want it to be.
Some other projects I'm thinking of:
Is it for a personal computer or a server?
It's better than nothing, surely better than proprietary software.
I've used Invoice Ninja for awhile. Works great. Self hosted but not foss.
"Cloud" storage is indeed more expensive. But depending where you live, you count the electricity cost in, and you use the storage 'only' for backups. Maybe it makes more sense to pay for remote storage in a datacenter. Check out Hetzner Storage Box, it's what I use.
If it's still too expensive, maybe ask a friend or family member (maybe someone that uses your media) to setup a nas at their home for backup purpose. (I use this for my media)
Make sure you encrypt your backups if you use a remote location for your backups.
You have to decide what's valuable for you. For me my media is, I can just download everything again, but the time I put in to have every movie the correct subtitles without ads, the correct posters, metadata etc. I value my time, I don't want to do it again if I loose everything.
Determined by Google, GrapheneOS will probably provide extended support like they did for the Pixel 4.
Not on Windows, maybe WSL? Popsicle from System76