IPS Connect Questions

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I have 4 IPBoard Forums and am considering using the SSO option of IPS Connect.  I do have a few questions for anyone that might be using it.  

I plan on doing a test with my least used forums prior to migrating to my bigger boards.  If I do a test of one forum as the Master will there be any issues of changing it to a slave later?

I know for sure that I have multiple users that have separate logins on each of my boards.  Many with the same username.  Will this cause issues?  Will the Master be the default for password if a user has accounts on multiple boards?

Does each board need to have Facebook login handlers enabled if it's used on the master?

I've only done one 4.x install to date and chose "Display Name" as the login.  Does this requirement need to be the same across all boards that will use the Master?  At this point I would be more comfortable with "username" than Display Name or Email address. 

Thanks for your time.