Do I still need to have a gateway of last resort for internet traffic on each L3 switch if I'm running OSPF internally? All my core switches currently have a Gateway of last resort. We are using an ASA 5520 that is not configured with OSPF. Should OSPF be configured on the ASA as well?
If properly configured, OSPF should be propagating the default route. You can have your ASA run OSPF or you can leave it as is with a static route.