It's not really any different - just the connection speed that's the issue. If you setup your sites and links properly within AD you can specify that replication should happen on a schedule rather than near-instant.
Things like a password reset are generally instant regardless, however new user accounts and other objects would depend on the schedule you setup.
Exchange at your HQ is normal. You won't see any Exchange tabs in AD U&C as the Exchange management tools haven't been installed. If you want to do Exchange management tasks you will need to install the administrator tools onto the DC. (Or your workstation along with the AD admin tools)
Key thing to is ensure that you have your subnets, routing, sites and replication all setup. Your users at the branch office should be using the local DC for authentication - however should anything happen you will still want your clients to authenticate even over the WAN.
Hence why you like subnets to sites and sites with DC's. You then set a "cost" for going over a link. As such AD goes to the DC with the lowest cost in the same site/subnet. If that DC is down it goes to the next one until it's out of DC's for the site/subnet then goes to another site e.g HQ)
Steve.
"They have the internet on computers now!" - Homer Simpson
