AlterBrains

If I understand correctly I can set-up a MasterSite which would hold the user database for, in my instance, JomSocial. I could then set-up SlaveSites which would share/pull the users from the MasterSite. It is also my understanding that ALL users would be shared - all, or nothing more or less.

My questions are;
1- Can I control the SlaveSite user access via the "multiple-profiles" feature in JomSocial?

2- Can I set-up a SlaveSite, sharing other component files and data from the MasterSite but NOT from Jomsocial AND install JomSocial on the SlaveSite, should I want this site to have it's own user database?

3- Is this an efficient/logical set-up? (please be gentle, just a novice here... )

- thanks, bojames

Yes, slave sites will use users database tables of main site, so all sites will always have same users.

1- Can I control the SlaveSite user access via the "multiple-profiles" feature in JomSocial?

Sorry, but I don't know if JomSocial profiles allow any permissions. I think not.

2- Can I set-up a SlaveSite, sharing other component files and data from the MasterSite but NOT from Jomsocial AND install JomSocial on the SlaveSite, should I want this site to have it's own user database?

Slave site can use own JomSocial database data, but this will also require own users data.

3- Is this an efficient/logical set-up? (please be gentle, just a novice here... )

Yes, JomSocial is often shared. But having a slave site with own Jomsocial data is suspicious.
Usually slave sites have most of master's database content. If you want independent Jomsocial - better have it in own separate hosting account.