Steps are easy when the user need to be associated with the new LDAP server and/or Tree.

You create a new LDAP directory object in GW ( under system, ldap servers ) and point this to the new LDAP server
In system, directory associations you select the new LDAP server and make sure you set the option "Override existing association" next to the rest of the info.
In the Preview screen you can deselect users if needed and then run the associate
This should associate all the users found in the new eDir tree and GW at the same time.

So this should cover 1-3

Question #4 the documentation is clear on this:

NetIQ eDirectory and Microsoft Active Directory are fully supported for use with GroupWise. Other LDAP directories should work successfully if they use standard LDAP attributes. See www.novell.com/.../misc_popups.html

Not seeing much more for #5 however you can test the above with only a single user to see how/what it does before doing all users, just deselect all but one user in the preview screen

We are having 5000 users associated with old ldap (e-directory), so is there any way by which bulk association can be done.

For testing our new ldap we can add new ldap under ldap servers and associate one user with new ldap.

We are having 5000 users associated with old ldap (e-directory), so is there any way by which bulk association can be done.

For testing our new ldap we can add new ldap under ldap servers and associate one user with new ldap.

I answered that above already:

You create a new LDAP directory object in GW ( under system, ldap servers ) and point this to the new LDAP server

In system, directory associations you select the new LDAP server and make sure you set the option "Override existing association" next to the rest of the info.
In the Preview screen you can deselect users if needed and then run the associate
This should associate all the users found in the new eDir tree and GW at the same time.

And later:

however you can test the above with only a single user to see how/what it does before doing all users, just deselect all but one user in the preview screen

If this is not the answer im not sure what you are asking then