Test Lab Active Directory: A few questions

Hello All.

I have created a test domain consisting of AD, Secondary, File server, Backup Exec, 2 workstations.
I am learning Group Policy along with Exchange. I would like to ask a few simple questions:

1.  Is there such a way to import a user file to populate the Domain with users? Or do I have to create each one?  (Just thought there might be scenario files out there)

2. Is there common settings I would add to each user, to make thm able to log in? i.e. Domain users.

3. If I have a user in Marketing OU, but they also need access or rights to Accounting, where do I put them?

4. How do I know when to put a user or a computer in an OU?

Thanks to all..this will get e going