[CentOS] migrating thousands of users to openldap in centos!

List, I have 15 Tru64 Database Servers in different places all over my
country, I also have thousands of users in all this servers, Now it's
really a pain to administrate all this accounts in all servers, so I
decided to install one CentOS server with openldap.

My questions are:
1. Is it possible to migrate all users from Tru64 to one Centos/openldap
server?
2. Do I have to install openldap in all servers in order to authenticate
local users even though the link (between the server and ldap server
goes down) and then replicate each other?
3. What is the best configuration of LDAP to fit this?
4. Is there any (Open Sorce) APP which do that?
5. Can I migrate all users using the migration tools from openldap soft
in Tru64?

Any help will be appreciate.

Thanks in advance
Regards,
Israel