Given everything I've read here -- candids, shallow DOF, etc., I'm thinking that, in addition to the group shots, you will want to single out individuals for candids. If you can't pop for something like a used Sigma 50-150/2.8, you'll likely want to use that 70-300 wide open and the 18-55 wide open at its longer focal lengths. You'll often have to stand off a ways because candids often demand it, and that will necessitate the longer lens. Don't worry about the DOF at f/5.6 on that 70-300 - it's plenty shallow wide open.
This is not a bad thing - using a long FL and a wide aperture to isolate the subject and get a compressed perspective in a candid gives an almost mystical quality to the shot and evokes curiosity in the viewer. When I was first getting started shooting events, I'd use a 75-300/4.5-5.6 on a 35mm body and I got great results with it.
When I was shooting these events with DX, my go-to lenses were the 18-70/3.5-4.5 and a 70-200/2.8, and I sometimes used a 12-24/4 and got right on top of a scene to get a unique perspective. If I were still doing this with DX, I'd pick up a 17-55/2.8 to replace the 18-70 for the short end to get shallower DOF. The Tamron and Sigma equivalents would be fine too.
I completely agree with the ISO-Auto idea. When I was doing this, I missed that feature on the D1X.