Exchange 2003 Message Store Cleanup

I definitely need some expert advice re: my Exchange server and possibly creating a new storage group, and separating out some mailboxes.  Here's the situation.

I am currently running Exchange 2003 SP2 (6.5 Bld 7638.2)
About 125 mailboxes in a single message store.  The drive which currently houses the message store & storage group is at about 90% capacity.  the priv1.edb is at 170gig, the priv1.stm at 98gig.  There are no limits set on mailboxes in this group.  Most are abouve 2gig, with a few at 10-12gig.

I have implemented an email archiving system (Barracuda Mail Archiver) and have begun whittling down some o the mailboxes.  But I really want to run an offline defrag to recover some whitespace, but at these sizes, I'd be looking at 24 hours minimum offline, which is totally not feasible.

So my plan is to create a separate storage group and break out some of those largest mailboxes to the new storage group, about 12 of them or so.  Hopefully after they have purged quite a bit as a result of the archiving solution.  Plus most of those high volume users belong to a specific business unit which would make sense to break out anyway.  So I'd move those to a new storage group on a different drive on the same system which has about 120gig available. And then run esutil on that group.

A couple questions.

1. Is this a good plan?  any other methods I should be considering for reducing the size of that huge message store?

2. Some guides or tips for migrating mailboxes to a new message store/storage group?  Anything I really need to be aware of before doing this?

3. If after moving those mailboxes, will the original message store be reduced in size, or do I have to run esutil against that as well to recover the space formerly used by those moved mailboxes?

Any advice, suggestions and cautionary tales would be most appreciated.

Thanks,

Ken