Docker is about uptime, consistency, integrity, CI/CD, etc. If you're just testing stuff, and won't notice a day or two of downtime, you can skip it for now (but it does make things easier once you learn it).
Always keep working backups of whatever you want to have on your server. Expect your server to get erased at any moment without previous notice, be aware of how much data are you willing to lose in case of a failed restore.
If you're processing user data, be aware of applicable data protection laws (if any).
Security is only relevant if you become somewhat popular, or you plan on leaving the project completely unattended for a longer period of time (don't, you will most likely get hacked). Otherwise, apply basic security measures and don't sweat it too much until you actually start having something worth protecting. Erasing and re-creating a server/instance from scratch is acceptable and secure enough in the beginning.