|Good thinking Dan......only problem I see is what happens if your router goes down?|
No matter what you do, you're still going to be struggling with a single point of failure unless you have enough money to have two separate internet connections and build redundancy around your network. Most small businesses can't afford this.
If you have a windows Active Directory integrated domain, my advice is to listen to wanderer......I agree with him 100%. The benefits far outweigh the risks (if you consider a server failure more.