Moving from DirSync to SSO (ADFS) after Staged Migration

Hi,

I'm in the process of Staged Exchange Migration from on-premise Exchange 2007 to Exchange Online.

I'm using DirSync, ADFS is not implemented because my local infrastructure is old and overloaded.

After migration of all mailboxes to Exchange Online I plan to decommission Exchange 2007 and leave DirSync operational for account and password synchronization between local AD and Azure.

After that I'm going to upgrade my local infrastructure (move to Windows Server 2012 R2 environment).

Is it a good starting point to implement ADFS and SSO between local AD and Azure AD?

Do I need to keep on-premise Exchange 2007 running even if there are no mailboxes on it in order to implement ADFS/SSO?

Regards,

Michal