@Katrin Schulz Thank you for your question.
In additional to the three items you listed, you must also backup the infrastructure. Please see here for more information.
From a PaaS (web app) perspective, please also review the backup options you have for additional backup protection of the deployed site on the web app here. This type of backup can protect you against DB corruption, failed deployment, etc. without having to rebuild your entire infrastructure using the above backups.
A good backup solution will encompass both the items you listed and the items listed in the docs shared in this reply.
Please let us know if there are further questions or concerns.