Replacing two servers with a single server - looking for input on strategy

HI,

One of my clients has a network with two domains:

Domain 1 - SBS2003 - 56 users

Domain 2 - WS 2008 - 23 users

Domains co-exist on single physical network but separated as separate VLANS via switches on the network.

Originally two servers to support two Exchange servers - one for each domain.

Both Exchange servers have been migrated to O365.

Both servers are pretty old and not fit for the future requirement of the organisation.

The plan is to remove the VLANs and create a single Network using a WS2012 server.

My current thinking (which changes almost daily as a new thought strikes!) is to start from scratch, with the following steps:

1. Configure the new server with a new domain name, with users and groups, copy the data from existing servers into shares on the new server, set up the permissions for user/group access to the data (the current security set up is a nightmare with permissions granted to individuals all over the place).
   If I have the server on the network at this point with a static IP address with DHCP, DNS etc not activated will I hit any conflict problems with the existing servers?
   Can I use Robocopy to merge the data on the existing servers with the data on the new server on a daily basis - i.e. only copy new / changed files?
2. Create login scripts to map appropriate drives and network printers to appropriate users / groups using group policy (better to use GP Preferences? - something I know of but only used sparingly)
3. Completely turn off the SBS2003 server, turn off the DHCP and DNS on the WS2008 server which I intend to use to support Spiceworks and Kaspersky Security Centre 9. As I shall not be using it as a domain should I 'demote' it in some way so that it is simply a machine on the network joined to my new domain controller?
4. Reset the network switches to default (creating a single LAN)
5. Turn on DHCP and DNS on the new server (all printers, network switches, and some other specialist devices will have reserved IP addresses in a specific range).
6. Then what I want to be able to do is create a ‘script’ that I can run on every PC , preferably centrally rather than having to visit every PC as they are spread over 6 buildings on a large site.
   I want the script to delete all user profiles on the PC (mix of XP, Vista and W7) remove the PC from its current domain and join the PC to my new domain.
   I am investigating ForensIT for this task - anyone know of any other way of achieving this?

This is the first time I have had to do this sort of thing on such a large (for me) scale. Any input from more experienced hands would be very welcome.

For example, would there be any advantage in migrating either or both of the existing domains? My gut feel is to steer of migration as I suspect that it will be moire trouble than it's worth??