The 831 will provide IDS for intrusion detection, firewall services for NAT, stateful inspection and port blocking, easy VPN for up to 5 users, IPSec and QoS as well as many other features.

please see the following link for more info on the 830 series router:

http://www.cisco.com/en/US/products/hw/routers/ps380/products_data_sheet09186a008010e5c5.html

as far as your thought process, it is not too far off. the biggest issue you may have is the 100MB port that will connect to your 'dmz' where your servers reside; is it enough to handle the anticipated aggregated bandwidth for the servers you mentioned.