It's going to be fairly manual given the duplication of accounts across machines.
I'm not a fan of using tools to perform such a migration, beyond bespoke scripts I might write for the particular situation. I feel like manual attention in such a small environment gives the best results. Call me curmudgenly, but I feel like there are lot of human judgement calls that come up in this kind of work. (To be fair, I've also never done such a migration with more than about 20 seats where we cared about saving any of the user's profile data. Migrating a peer-to-peer hell that big sounds nightmarish, if you ask me. Automated tools, if properly tested, tested again, and tested a third time would probably make a larger migration a lot easier, but the number of clients would have to be a sufficiently large value to make all the time in testing pay off.)
I'd start by getting the server computer setup w/ the desired folder redirection, roaming user profiles, etc. Get a test machine joined to the domain and verify that everything acts as you'd expect it. If you need to do any customization of the new user environment get your Group Policy setup to do so. An ideal situation is such that a new user's roaming user profile doesn't require any of that "an Administrator has to logon the first time and setup things in the registry" silliness. I "break" SBS 2008 and provision redirected folders manually because I think the default method is silly. This has the advantage of giving you folders to put the user's documents, etc, into before they've ever logged-on.
If you can throw away the individual users' registries you'll have the cleanest migration. (Crappy apps are notorious for storing absolute paths in the user's registry and having to do mass search-and-replace across registries is no fun.)
If you can't get away with throwing out their registries then you'll want to either get cozy with USMT or, use the GUI to copy the local profiles to the domain profiles, or manually hack the permissions stored in the NTUSER.DAT. Personally, I'd throw out the registries, since they're likely gunked-up with absolute paths and such hooey anyway.
Assuming that you don't have file version conflicts to worry about between the various machines I'd just pile all of each user's files (Documents, Favorites, perhaps Cookies, maybe AppData if I felt like there was something useful there) into their newly-created roaming profile / redirected folders on the server computer and move a copy of the locally-stored profile to some offline media for safekeeping (and to prevent them from falling back to the local profile w/o telling you and creating an even bigger mess).