Replica Active Directory domain controller on Windows Azure

Hi,

I want to extend my on premises active directory and Exchange to cloud.

This is new environment greenfield. 

I want to setup on premises AD and Exchange and i want to extend my AD on Windows Azure VM as replica.

Exchange will be hybrid deployment in O365.

My question here is:

1) If i configure replica by extending my on premises AD, do i need to have DirSync in on premises / Clode

2) Do i need to have AD-FS, does it really required.?

3) How my authentication will work on both on premises users with cloud users to access exchange resource.

Regards

Ganesh Prakasam

Ganesh P