No. You can still work with InfraWorks models locally, and directly share model data using conventional file-sharing processes. But if you want to share models for online collaboration, you will need an Autodesk Docs account and permissions to an Autodesk Docs project.
You can download an existing cloud model and publish it to an Autodesk Docs project from InfraWorks. Alternately, you can download models for offline use.
The current system of user permissions and groups will be replaced with Autodesk Docs projects and project members. Autodesk Docs account administrators can create projects and assign project administrators. Autodesk Docs project administrators assign roles to project members and manage folder permissions.
The current web and mobile applications will be replaced with the more powerful Autodesk Docs mobile application for viewing, reviewing, and mark-ups of your InfraWorks projects.
Yes. See To create a model with Model Builder.