Your design does not meet any security standards, as one of the major factors is the single point of failure. There is no internal firewall to protect the internal/private network. The router in between will not be able to protect anything if the firewall gets compromised and it will open up the doors for attack. I would suggest you go through the above resources to get a good understanding of the design principles. Once you understand the principles you will be able to identify the problems and rectify them accordingly.
This was first published in September 2005