As it was already said. Docker is not virtualization. The number of Containers you can run depends on the containers and what applications are packaged in them. I am pretty sure you can max out any host with a single container when it runs computational heavy software. And i am also pretty sure you can run on any given host thousands of containers when they are just serving a simple static website

Have done it via bash scripts for years. Never had a problem. Since a few months i use https://github.com/qdm12/ddns-updater

You recall wrong. ECC is recommended for any server system but not necessary.