I think your basic idea is sound, but you need to think what you’re going to use for the connection between the 2 machines. Are you thinking of using an internet/broadband connection? Then you’ll probably need to look at getting a firewall setup on each end, with a VPN connection between the machines (maybe this infrastructure is already in place at your site?). You shouldn’t really need to have dual ethernet cards in the machines, as long as your network is setup correctly with routes between the 2 machines.
If you setup the firewalls correctly you should be able to close down everything apart from DDM and whatever transport mechanism you use for spooled files (SNADS, remote writers, etc).
In any case, I suggest you talk to someone with knowledge of setting up networks and firewalls for more detailed advice for your particular situation.