First of all, the most important part to any network design is to have redundancy setup on it. Always have a back up plan. Different service providers that come into your network using BGP, multiple routers and switches that direct traffic to your users. You will never know when something might fail on you. Once the in house network is setup, you would need to think about a DR site.
So, ALWAYS HAVE A BACK UP PLAN! and think Redundancy, Redundancy, Redundancy.
– 2 or more internet providers
– BGP protocol setup on your routers
– multiple firewall/switches
– multiple connections on the server