Change from AD to openldap

I am in the process of planning the move from AD to openldap. I have used sAMAccountName for internal username and plan to use uid on openldap. username and passwords are the same in both ldap servers. In my head the process should be as following:

Remove access to the webserver for all users (but me)
change the config of ldap from AD to openldap and use uid as account mapping.

And then comes the parts I am unsure of.
Should I delete everything in ldap_user_mappings and things will map itselfs to the right folder and user the next time they connect? Or how should I make shure we dont end up with thousands of _1543 - accounts with no content?