Hello,
Answers to your question see below 
How do I make sure my QGIS project goes directly to my organisation plan?
-Once you transferred your projects to your organization (Project settings → Transfer ownership of this project), QFieldSync will automatically save changes on your project there (QFieldSync shows the project owner)
Can I just use Qfield Sync and it automatically loads into the Organisation Plan?
-once, the project is created in your organization, you can have access to it via QFieldSync.
Can I delete the Pro Plan that seems to be there?
-yes, edit profile->billing->change->subscription
If I create a project inside the organization plan, how do I get my files created on QGIS into that project?
-Via QFieldSync like before
Do I also need to add the other collaborator or should they automatically have access as they are a member of the organisation?
-They will have access to the projects. You can find more information about it here: Basic concepts - QField Ecosystem Documentation
I hope that I have answered your questions!
Kind regards,
Zsanett
Imported from GitHub comment by @ZsanettMed on 2023-02-27T09:36:43Z