Is it required/recommended to have a router in your network topology? example Cable modem => SonicWall => Switch
The short answer is no. Dedicated routers are becoming increasingly more rare in production environments. A lot of small office / home office deployments now use their firewalls as a router. Almost every firewall is capable of routing (transparent firewalls being the exception) so having a second device is redundant. In MPLS networks it is not uncommon to see a Layer 3 switch used as the router. However, in environments where you need to do media conversions you will still require a dedicated router. So if you are deploying frame-Relay, T1, E1, ISDN, or other serial based communications you will need a router as you don't typically find those interfaces on firewalls and switches.
Hope that helps,