Dear Elsa Victoria Aristizábal,
Good day to you!
I hope you are doing well. Thanks for reaching out to our Microsoft Community Forum. We will be happy to help you.
According to your description, you would like to purchase Microsoft Project Plan 3 for institution. You would like to know if it is possible to pay in advance for three years. Generally, Microsoft Project Plan 3 is billed annually or monthly, but the payment page does not provide explicit details about a multi-year payment option.
Also, the Project Plan 3 subscription includes both Project Online and the Project Online desktop client. Here is the subscription details page for your reference: Compare All Planner Options and Prices | Microsoft Planner
Additionally, apart from Windows, our organization plans to use only Microsoft Project, excluding other Microsoft products. However, to enhance productivity and collaboration, the organization may consider a Microsoft 365 subscription, which includes Office apps, Microsoft Teams, Power Platform for custom app development, and more.
With Project for the web, one user can update project information created by another user, provided they have the necessary permissions.
If you have any questions, please feel free let us know for further assistance.
Thank you for your understanding. Your cooperation and contributions are greatly appreciated.
Kind Regards,
Nahid Sultan