12.17 Can another person only administer the project, but not have the rights to perform other actions in the account (not related to the project)?

Yes, another person can be granted rights only to manage the project.

Go to Projects and Activities > My Projects and select Project settings > Administration rights. At "Grant rights to another user", you can check the box and grant a person the right to Manage the project (all rights).

The person you are granting rights to, should have an identified Paysera account.