Yes you will need an AS Interlink cable for both units ...

Waypoints created on 1 unit are physically transferred into the Interlink and the other unit memory...

1 GPS module can be used for both units ... But more accurate waypoints would be obtained by having a separate GPS antenna as close to each xducer as possible ...

Map data cannot be shared by any core HB units ... You will need a card for each unit ...

Greg will correct me if I stated incorrectly ...(I'm not well versed in Interlink)...

Rickie