Ubuntu doesn't allow pip to install system wide stuff anymore. You can solve that by installing everything in a pyhton virtual environment.
But for real, use Docker/Podman instead. It's a lot easier, especially if you're managing several applications!
The Beeline is definitely powerful enough to run a hypervisor, so I would do that if I were you. Proxmox is a very good product and easy enough to use. Personally I use Harvester (with Rancher) but that might be a bit daunting if you've not used Kubernetes before.
I would recommend running Proxmox as your OS, spin up a few Debian virtual machines and run your services (Nextcloud, plex/jellyfin, ...) with Docker containers. I would personally use Podman, as I think it's the simpler one to use, but there might be more documentation online for Docker, I'm not sure. But do definitely use containers! You'll thank yourself in 6 months.
For reverse proxy I would suggest using Traefik, especially is your using Docker/Podman. But there are other good solutions like Nginx Proxy Manager, which has the advantage of being very easy to use. But I do run Traefik on every Podman server I have or any Kubernetes cluster. That way I can just have a wildcard DNS entry for an IP and then every proxy route will just work, whitout having to touch the DNS further.
Also, just a general tip: look into how you can deploy everything using a GitOps flow. Whether that just be with Ansible or more specialized solutions (Kubernetes with ArgoCD or FluxCD is very well suited for this). Look into Terraform/OpenTofu. This last point is nowhere necessary, but if you ever (like me) get tired of forgetting how you setup your infrastructure (virtual machines, application deployments and configuration, etc) you'll love GitOps.
Oh, but do definitely look into Ansible for configuring your servers. It will save you a lot of time in the long run.
I think that's kind of what they meant. I've also selfhosted Nextcloud for years, but I only use file sync and calendar/contacts.
Lately I've been feeling that Nextcloud is too big and clunky for just that. Like it's something I'd love to setup at work or for an org, but that it "feels" to heavy for home use these days.
I need to check out Radicale, I think.
OpenSUSE MicroOS or Fedora CoreOS. If you'll be using containers you'll have a great time. If you don't want to deal with transactional systems, then there is literally nothing I'd rather use than Debian.
Totally get The Foreman. Worst piece of garbage I've ever used.
I do use ansible to set up my own repository management/lifecycle environment servers nowadays, specifically to get rid of Foreman.
Why do you dislike ansible? Got to say that I love it, especially compared to stuff like Puppet and SaltStack.
I'm a sysadmin with a background in computer science, so I'll say any fucking enterprise software on the planet. It's all trash and annoying. I'd run Debian every day of the week over Windows or RHEL and the likes.
I never knew how much I love and appreciate open source/free software until I worked in enterprise...
"But VMWare PERFORMS BETTER than Proxmox!". Yeah, with 10 times the chance of making you depressed.
The Foreman/Red Hat Satellite. Many people wont know what it is, but it's the worst, bugiest, slowest piece of garbage I've ever touched.
Also Windows... I'm a Linux sysadmin but my work computer "needs" to use Windows and I've never disliked it as much as when I've been forced to work with it. Why is the virtual desktop experience so trash???
Got to say I really like the Fold. It's professional yet cozy
I haven't used Jellyfin with docker before, just with podman and as a pod in k3s. Both work great and are easy to maintain. If you're more familiar with podman then docker, then I'd recommend using podman.
Just make sure to mount your volumes with the :z or :Z flags. I have disabled SELinux on servers in the past, but never when I've just used podman containers, since "it just works" with SELinux. Literally never had any problems with containers and SELinux.
I'm currently running Jellyfin on a VM in Proxmox and have been for a long time, it works great. My storage solution isn't glorious, but it is simple. I just have a Debian LXC container in proxmox that bind mounts a large disk and exposes that through an NFS share. Then I've installed jellyfin with Podman/Docker on a VM that has that NFS share mounted.
Also, a lot of people have already said this, but Podman/Docker only looks intimidating before you use it. It's A LOT easier to get applications running then using the "traditional way". The only thing that could potentially increase complexity for you is to expose a GPU to the docker container. But since you said you don't have a dedicated GPU I'd strongly recommend using a docker container for the job. Once you've used it, you'll never look back.
KDE Plasma used to have one like the one on the right a few years ago, and I was so glad when they ditched it. I strongly prefer the organized look of the left one. I always had a hard time finding anything in the old KDE/MacOS settings.