Seeing your issues with your current setup, the best thing to do is to start fresh.
You can keep a copy of your OD but I wouldn't use as a starting point.
Any data in calendar of addressbook for your users should be saved as a local copy and not be reimported again.
That way any errors/issues will remain local and will not interrupt the new server.
Remove any local references/accounts connected to the old server and reboot the clients.
Setup a new server with MountainLion client, purchase the new MountainLionServer and setup DNS, SSL certificate for all your services and the push notifications will be created new when you supply your AppleID when starting Profilemanager. Then activate the needed services.