Here’s a couple of good videos that gives you an overview of how Office365 will work with SBS Essentials.
This first video shows you how you can manually set up the integration between SBS Essentials and Office365. At the moment, this is the option you’ll have to use until the Office Integration Module (OIM) for Office365 becomes available.
This video shows you the current (pre-release) Office Integration Module (OIM). It has some nice features and integrates nicely with SBS Essentials. Importantly, it doesn’t provide any AD synchronization, it simply allows you to easily administrator Office365 from the SBS Essentials console.
This video shows you how to integrate your custom domain with SBS Essentials. You will note that the Office365 servers need to become your DNS name servers. This means you’ll have to use Office365 to edit or add any records you have for your domain. The video shows the example of setting up the remote access URL on Office365.
If you are planning to install SBS Essentials and integrate it with Office365 then I’d suggest you take a few moments to have a look at each of these videos, after which you should have a much better idea of how it all integrated together.