Get a few 4 and 6 foot straps for carrying gear -- I love all the loops for this on the Aire IKs. You will want some longer starps if you are going to rooftop the inflated IK. You can never have too mant straps!
I use caribiners all the time, for example, to attach a water bottle to a strap (I don't trust the drink holder on the back of the seat by itself to hold a bottle in rough water or overturned).
Best way to see if you "need" an electric pump is to not get one and see how you feel w/o it. Because I have garage space, once I inflate an IK for the season, I leave it inflated and only use a k-pump (I do have an electric pump that is handy for full inflation -- but I also have larger inflatables that make it even more handy!). Oh, I actually keep my Aire IKs inflated all winter, so they haven't seen an electric in years!
I also have an inexpensive 4-piece spare paddle that I bring along for safety, but actually have never had to use it.
That boat should rock! I saw a couple of them producing great fun on the Main Salmon a few weeks ago.