24 experienced people to run the MF with is about as good as you're going to get as a learning experience. Do it. Take the Ik and the 12 footer with a frame. You should be able to carry a decent amount of gear in the 12 footer. Talk to your TL and make sure they are good with your boat choices. Let them know that you'd like to follow someone down who knows the lines. The IK will indeed be helpful to get the bigger boats unstuck. We bring rookies in IKs on low water MF trips all the time and they have a blast. Cramer rapid once you turn the corner onto the Main Salmon will be your biggest rapid, but like C-Dog said....hit it straight and go hard.
If your TL balks at the 12 footer/IK idea, then go back to your original choice and take the 16 cat. You will never get a better opportunity to run & learn the MF as this. I was only a moderately experienced rafter the first time I did a MF trip in a 14 foot cat. I followed an experienced cat boater down. Learned a lot & had a great trip, even though I was nervous about it.
"We are all visitors to this time, this place. We are just passing through. Our purpose here is to observe, to learn, to grow, to love....and then we return home."
Australian Aboriginal Proverb