We've walked through much of this over the past few year. Like @tlphipps said, email first is pretty much Microsoft's idea (along with AD). The newer Azure AD Sync tool is really simple to setup and does a lot more.
Moving to Exchange Online was honestly rather simple. We did users in waves of 15 because I was afraid we'd have hiccups each time, but we didn't. I could have done them 50-100 at a time and been fine. I just let people know a few things:
- They'd need to restart Outlook
- They'd need to remove and readd their account to their phone
- They'd need to enter their username and password into Skype for Business.
I did enlist the help of Mirazon as we walked through this process. They fulfilled more of a consulting role here, where I could ask questions and get answers. We migrated from Exchange 2010, so there were some known issues with that. Nothing major, but things that it was good to know going in (like having to run the hybrid setup tool twice to get it to take).
OneDrive for Business
After we did that, we really started pushing OneDrive for files storage with our users. The timing on this was helpful because Microsoft was actively updating their OneDrive client for both PC and Mac. With the latest release, it will even let you sync files from SharePoint Online, which is awesome and the last feature we were really waiting for.
SharePoint has been the slowest thing we've rolled out. We moved a couple teams to it to replace our shared folders, but without the ability to sync, it was always a burden to get them to know how to access those files.
Like I said above, with the new sync client this has become much easier.
Further, with the launch of O365 Groups, SharePoint has become much more friendly and Groups gives an united interface for files, conversations and more. We're in the process of moving several old Exchange distribution groups to O365 Groups and the teams love it so far.