Migrating components off Windows SBS 2003

Here is my scenario:
I inherited an old server running Windows SBS 2003.  It is the sole DC in our single domain.  It does the DHCP, DNS, IIS, hosts exchange, and acts as a file/print server.  The primary means our employees access their email is OWA.  We have only a single storage group and do use quite a few public folders.  

I want to eventually move all this off the SBS and decommission it.  This doesn't have to be done overnight and the SBS can continue to run for several months if necessary.

I intended to put Exchange 2003 on its own box.  Make another new server a DC and install DNS and DHCP on it. Remove DHCP all together from the SBS.  Turn off all exchange services on the SBS.  Eventually, assign the new DC the master roles, GC, etc. and decommission the SBS totally.

If I am understand everything right.  I set up a server, install windows 2003 and patch it up then install my new exchange server 2003 enterprise version on it.  I then replicate public folders to this server and give that several days to happen.  After the public folders are replicated I can move the mailboxes.
Set up my second server, install windows 2003, give it DC, DNS, DHCP roles, etc.  The DNS is AD integrated so I really shouldn't have to do anything.  I could set up the DHCP scope identically to how it is set on my SBS then deactive the scope on the SBS.  If I understand it right, basically everything except giving this new DC the schema master roles.

When I'm ready, (and make sure everything is moved,) I can assign those master roles to the new DC and just take the SBS off the rack?  This is where I'm getting a little fuzzy.

I read a little about transition packs and partial-swinging, etc.but I'm not really sure why all that is necessary.

What I'm looking for here is some input as to the validity of my plan and any difficulties I can expect to encouter.  As well as any suggestions on how I can accomplish this better.