Sounds like a great trip you guys are going to take. I have not run Cataract so I do not know how portagable the rapids are. But, if you run Waterton and Westwater in a playboat, you will probably be okay on Cataract.
Paddling a loaded boat is a little different than paddling an unloaded boat. Everything takes a bit more time to get somewhere and turn the boat because of the added weight. After the first few hours of just paddling you will start to get a feel for how it's going to handle. I would recommend taking a few practice rolls also to get a feel for how the boat is going to roll with the extra weight.
As far as the self support, pack light and try and keep everything in quality drybags. Especially your sleeping bag and food. Try not to have anything on the outside of your kayak because it makes rolling tougher.
I'm a class IV boater, I paddled a loaded kayak for the first time in December. Seven of us spent 9 days self support kayaks on the Grand. My base weight for all my gear was 50 lbs. groover, food, camp setup, breakdown, and clothes. After the trip I realized I could have possibly shed 5 lbs of gear I brought and didn't need.
I kept my meals simple. I brought 10 days worth of food. 20 packets of instant oatmeal then added 1/4 cup almond slivers and 1/4 cup dried blueberries (2 packs per day). Lunch was gorp or a pb&j. Snack were kind bars (I brought 30 only ate 10), 3/4 pound of beef jerky, and dinner was 10 boxes of Kraft Mac & cheese (1 per night). I always felt full an had plenty of energy. I have to say by the 8th Mac and cheese dinner I was ready for something different. Gained a half pound on the trip.
After paddling everyday all day you will feel pretty good in your boat at the end. Have a great time!
Edit: I forgot to say that is is also easier to punch holes and big waves with a loaded boat! Scout the drops, stay in the tongues, miss the holes and t up to the big waves. On the Grand the rapids looked chaotic but boated much easier than they looked.