Hello there... in order:

1. Later this calendar year we will get to feature parity with New Teams features

2. Our adoption strategy is very similar to all new capabilities.  Use our resources at https://aka.ms/NewTeams to share the "faster, simpler and more flexible" messaging.  From that page you can also see my video talking about New Teams benefits that you can use to identify the user communities who should have it first. 

3. The best practice since we are still in preview is to release it to early adopters first and people who can understand switching back and forth with the toggle.  Rolling it out to the rest of your organization can be based on their use of features that are not yet available.   To learn more about this you can join our Champions program and hear more in our monthly meetings at https://aka.ms/M365Champions

4. Please refer to our https://aka.ms/NewTeams page for the overview and from there you can go into our administrative documentation for more details. 

Thank you!