There's a lot to cover here but I'll start with the simplest question to answer. You'll get very wet in an IK, AKA ducky. Dry gear is very expensive and as such is typically only worn by those who often paddle in adverse weather conditions when getting wet is a safety hazard as opposed to a mere inconvenience. There are much better places than here to hash that out, but basically there are two types of dry wear; a drysuit, which will cost anywhere from $500 to $2000 depending on quality and whether you can find one used and dry separates which include dry bibs or pants and a dry top which will cost anywhere from $500 to $1000 or so, again depending on quality and whether there are used items available. Another option is semi-dry or splash wear which is much less expensive and does a pretty good job of keeping you dry unless you come out of your boat. You can easily put together a semi-dry outfit for a couple hundred bucks. I personally use a wet suit and splash top combo when a dry suit isn't necessary (except in warm conditions when I just wear board shorts) but I paddle a canoe, not a ducky. If you're just looking to stay dry inside your ducky splash wear would probably be fine. Just keep in mind dry and splash wear are designed to keep you dry, not warm, so you'd need to layer appropriately.
Now to the question you didn't ask. Think it over carefully before you decide to buy a tandem ducky. They're very susceptible to wind, so if your only reason for going that route is portability you'd be better off with a tandem canoe IMO.You could easily keep one out of the way on top of your truck and it wouldn't be near the PITA to deploy that a ducky would and it would last a whole lot longer, plus you and your gear would stay dry as long as you stayed in it and you could even get one that would work with a trolling motor all for what you'd pay (or less) for that Sea Eagle. That said, if you're determined to buy a ducky please don't buy a Sea Eagle. You can do a lot better for the money. Check out Aire and NRS.
