Side imaging requires exterior transducer placement, correct? I did a little research and couldn't find anything that says you can mount the transducer inside the hull and still have the SI or DI work.

Is there a min/max speed required for SI or DI to work properly? It should work fine under 3 miles an hour (which is what most of us paddle at, or less). You may need to adjust your chart speed though.

It will be installed on a Slayer Propel 10. - Can't help you there.

Will a standard 7 or 8 amp 12V battery be sufficient for units like the Helix 5 SI? I run mine on a Deer feeder battery and can run it on an all day trip.

Does the Helix 5 come with sonar contour maps, or is a card needed? That is an additional purchase. $125 - $150 for the chip.

What is difference between Helix 5 and more expensive units with same screen size? The 788 does not have SI and it is $900. I asked the same question when I bought mine. The guy at Cabella's told me that there is no reason to buy the more expensive ones for a kayak. They don't offer any benefits over the H5 (specifically talking about the Hummingbird brand).