We have started to add postal codes as alternate names with the pseudo iso language code 'post'. This makes sense if section of populated places have other names and other postal codes.
Otherwise you can send me an excel or other file and I directly update the database with it. A wiki-entry form is not yet implemented for the postal codes tables.
The lat/lng are empty if we haven't found a place with the same name in the main database in the correct neighbourhood and if we don't have enough information for an estimation.