Thanks.
We havent decided whether we want SSO or not and to implement adfs just yet, can ADFS still be implemented after we complete the migration and decomission the exchange etc.
if we do go ahead with SSO, are there any steps to covert onpremise user to MEU for Exchange 2010 => step 2 Convert on-premises mailboxes to mail-enabled users on community.office365.com/.../835.aspx, this only has 2003 and 2007.