Just my opinion here… But, installing onto a KVM type VPS is probably the best way to keep a long term installation.
This allows you to increase server resources (CPU, RAM, SSD) without affecting the running server. When you have been running a ERPNext server for a long time you might actually wind up growing the business that it supports and therefore need to be able to expand the system resources to meet the increased demand.
Docker images tend to try to keep everything in the container (including the database) and at some point it will become to large to handle within the container.
There are several ways to setup a container that would allow for the database to be in a separate server, but if you are going to go that far then why not just be simple about it and install from scratch on a good VPS.
This way, if you discover a problem in the installation later you can fix it yourself. In a docker image that is not really an option.