VisPlan runs as an app on Microsoft Teams, which is part of the Microsoft 365 family (formely known as Office 365).

Yes, as we run in Microsoft Teams, utilize the Microsoft user login credentials and all data you enter is stored by you, it is required to have a Micrisoft 365 business subscription. 

You need to have an active Microsoft 365 business license, but it’s absolutely possible to use both Google Workspace and Microsoft 365. It requires some configuration by your IT-admin. 
https://jumpcloud.com/blog/integrate-g-suite-microsoft-365

Yes, it’s very simple to set up a Microsoft 365 domain. You can even have it set up for free 30 day trial in minutes. There you can install VisPlan and try it for 30 days without any risk of exposing any real corporate data. 
https://www.microsoft.com/microsoft-365/try

Yes, for large corporations we offer a SharePoint version that can be used in the cloud, hybrid or on premise. Please contact our Sales department for further information.