High availability storage is what the Ceph integration is for.
Edit: though it's kind of a pain to set up and probably way overkill. A separate TrueNAS or similar appliance with a 10 gig uplink will be easier and probably just as reliable for your use.
Sublime Merge is what I use at work and is the only Git GUI I've had good luck with. It's not free but well worth the 50 bucks, or you can use it with the nag screen indefinitely like Sublime Text.
This is not a good idea unless you really know what you're doing. High capacity batteries and high power circuits are pretty dangerous and there's a surprising amount of complexity to build a reliable UPS. You'd probably have better luck modding an existing UPS (say from a flea market) to use a bigger battery if you are really desperate to save every dollar.
Plus making it yourself you probably won't save any money unless you already have all of the tools required, which is pretty extensive if you wanna do things right/safely.
I personally dislike the Plex apps, but yeah its native support is unmatched. The official Jellyfin app for Android gets the job done but isn't native. However, Findroid seems like the future to me on Android and I use the Kodi plugin on my TV (which is amazing).
Yeah setting up a reverse proxy can be confusing, I still struggle with it sometimes. You can get away without it, but when you have your basic setup working then it's great to have.
Other people have said lots of useful things so I wanna just add on: nginx proxy manager is really useful for this. It's a webui that automates reverse proxying with Nginx (so that you can host multiple pages on the same machine/port) and also centralizes managing SSL certificates, including automatically obtaining them from Let's Encrypt.
Related question for those of you running Proxmox... how do you back up the Proxmox host itself? Last time I looked into it the recommended solution was basically manually copy a few folders in /etc or do a full disk backup but that's pretty unsatisfying. Currently I can easily restore any VMs that fail from backup with a few clicks, but if the SATADOM I installed Proxmox onto failed it'd be kind of fiddly to reconstitute and restore all the other settings/networking/etc.
I use pfsense's HAProxy integration and a combination of Cloudflare or Lets Encrypt certificates for external stuff. For internal-only stuff I have a root CA I distributed to my computers that I use to sign certificates. My docker box that serves most of my internal stuff has an nginx-proxy-manager container with a wildcard certificate so that I don't have to sign one for every new subdomain on my docker host, and the various containers with services in it talk to it over a private docker network. Buying a cheap domain and managing it through Cloudflare simplifies a ton of stuff.