You seem to have it all figured out already.
The little I can add is as follows:
1)Get a router modem, the performance is better and net access for the rest of the machines isnt dependent on the server being up.
2)Get a Firewall <netgear FVS318> you will cry buckets in the future if you dont.
3)Put your printer on the server. It ill diminish the load on your workstation (okay its not much of a load but its something)
4)As far as you are concerned you cant network a scanne, they need to be bound to a machine (...there are ways around it but they are fiddly and messy options)
5)Load DHCP on your win2k server
The rest of my words might sound flippant but thats not intetional I assure you..
If you want active dirs just set it up. Do you need step by step instructions?
If you want a 5th machine, just plug it into your switch !!
Its a s easy as pei (I mean pie !)
Map a drive to your shared folders if you want them, thats probably the easiest thing to do !!