Wiskers,
I have a 997CSI. I have a couple of so called "buddies" that have or have had the 797csi. There is only one transducer to mount. The side image and the regular sonar comes from the same transducer. The GPS antenna is external, but it comes with the unit. You may need to buy a mount for the antennaif you do not want to drill a big hole in your boat. I don't know where they got the unit at or at what price. I would mount the transducer on the stern of the boat. I believe 80-90% of the people are mounting on the stern. The turning of the trolling motor with the transducer mounted on it disrupts the side image. Your hotmaps card should work fine in the 797. If you plan on fishing alot of different waters out of your region then the preload would probably be worth it. I believe the 07' cards from Nav. are 1' contour intervals and I heard that the 06' Nav. are 5' contours. I'm unsure if this is completely accurate. The unit will also look downlike a regular sonar. On the menu there is an option to have only regular sonar, side image only, combo side image and reg. sonar, you can also use a combo with the sonars/images and your map. I like mine so far but I'm still learning. Check your PM. Todd