Building out a network for your office (How do you start?)

Can someone outline the basic steps on getting a network running for a company? My guess is it works something like this.

1. Contact ISP to request a business network
2. ISP provides you with a modem/router and public IP
3. You place a firewall or switch infront of the router
4. You set up NAT (how does this work exactly if this is the correct step)
5. Connect your network devices to your switch