The javAPRSSrvr sysops (aprs.net core servers and aprs2.net servers) use port 14580 as a user-defined filter port (no default filter). If no filter is applied by the client, it functions properly for IGates (maintains a last-heard list for the client and performs proper message and related posit passing in addition to any messages and related posits for the logged in client). A filter is not needed for proper IGate operation and will make your IGate software use much less resources than a full feed simply because there will be very few packets your IGate will have to process.
Adding filters is best suited for GUI clients because you want to see more than just what you might see on RF. Standalone and non-GUI IGates are best used on a user-defined port as you describe (port 14580) with no filter specified. This will provide proper IGate operation while minimizing impact on your system and your bandwidth to the Internet.