Newbie going self-hosting

Right now I've almost completed the assembly of the hardware.
Looking forward to diving into the software part.

Check me, please, if I understood correctly all the relations

Could this scheme be easier? How to optimize the plan?
Where in this scheme goes portainer and do I need it at all?

All the comments and recommendations are welcome. Good links could be helpful too.

@ignatiykalakutskiy welcome to the VHT forums! And, i think you have come to the right place as I know there are a lot of talented self-hosters who frequent the forums and will have valuable input. I think everything you have mentioned makes sense to me. Starting slow and without much money invested is a great way to get your feet wet  and even see if it is something you want to spend more money on in the future. 

The good news is, there are a lot of great resources online today (Amazon, AliExpress, and many other online vendors to get things fairly cheap. Today's hardware goes a long way also, especially if you are running mainly containerized self-hosted services.

It looks like that is the approach you are pursuing here. I do think you have the logical layout understood here - hardware > Proxmox > Docker > containers. I would start with Proxmox and install a good Linux distro like Ubuntu to create a Docker host where you can run your containers. 

Can you run Docker directly on top of Proxmox? Yes, however, a VM will give you an easy rollback mechanism (ability to create backups, take snapshots, and many other features that you won't get without the VM abstraction layer. 

Also, once you have your Docker host or hosts running in VMs, Portainer is its own Docker container that will be able to manage the other Docker containers on your Docker host. If you install Portainer in one of the hosts as a container, you can install the Portainer agent on the other Docker host to have it managed by the single Portainer instance.

Let me know if that makes sense. Again, great to have you here in the forums!