Without a link to the manual, I don't know what the "Custom" through "Off" settings do exactly. But that doesn't really matter in this case, as the best advice I can give is to leave everything you don't know or understand at the default settings. Assuming that "modem" also contains a router and switch (and possibly an access point too), it is the NAT router
functionality that provides the firewall. Manually blocking any of the specific ports you listed will unnecessarily cause trouble for applications that need them. The only "modem" or "router" settings most people should be concerned with are to enable WPA/WPA2 security on any included wireless access points. Scott.