Hello, Guys!
I will move my mailbox from Exchange Server 2013 CU5 to Office 365 and i was studying about this migration.
First, sorry for my bad english. I'm brazilian.
1 - I have some Department Mailboxes, for example: HR, Support. I want transform it to SHARED Mailbox. How can i migrate my mailbox to Shared Mailbox? Is possible?

2 - i'll use ONLY Microsoft AADSync and not ADFS. What's difference between use ADFS + AADSync and only AADSync in hybrid environment?

3 - I read that is needed to import a third-party certificate on Exchange Server 2013 Servers  before run Hybrid Config. Have any step-by-step of how to do that? What is pre-requisite about certificate in hybrid migration?

THANKS!!

1.  Convert them to shared mailboxes on premises first.  Then they'll be shared mailboxes in the cloud.

2.  They're two different things.  AADSync synchronized your on-premises directory objects with Office 365.  AD FS facilitates authenticating to Active Directory.  If you configure AADSync to perform password synchronization, you don't need AD FS, but there will be a hash copy of your passwords in the cloud AD.

3.  The only prerequisite for a hybrid configuration is that the certificate comes from a source that Microsoft trusts.  Go Daddy is among the cheapest and their certificates work from my experience.  There is plenty of documentation how to do this on the Internet.  Just search.