Ingrid,
when we started out over 5 years ago, we had Canon D30s and Sigma 28-70 F2.8 and Sigma 70-200 F2.8 lenses plus 550EX flash units.
Since then, I've gone to the Canon 17-40 F4.0L as my primary show lens and added the Canon 50 F1.8 as my portrait lens.
For formals, the short zoom has always worked fine. It allows you to frame as tightly as possible without having to move around a lot. While the image quality of the Sigma 28-70 is not outstanding, it's fine for my primary product which is 8X10 prints. The 17-40 is sharper and goes to 11X14 without any problems. For me, the convenience of the short zoom is essential for the ring shots and podium shots since they always involve a judge, handler, dog and usually some show official or owner.
The Sigma 70-200 Zoom is a pleasant surprise. It's just as sharp as the Canon equivalents and was less expensive. It focuses fast, is pretty easy to handle for action shots and it produces lovely images. At 70mm, it also works very nicely as a portrait lens.
The Canon 50mm is just a wonder. It is the sharpest lens in my bag and it's unbelievably lightweight. I've made 16X20 prints with it and they are lovely. Not bad for a $75 lens!
Sounds to me like you have pretty much all you'll need short-term for camera and lenses. I love the Nikon system and they make great optics. When we opted for the two Sigma zooms, the f2.8 maximum aperture was important. What I find now is that I shoot 95% of my show stuff (including action) at F8 because that tends to be the sweet spot of my lenses and I compensate if necessary by using highter ISO.
My suggestion is to use what you have until (or unless) you find a significant short-coming in your lens arsenal and then add what you need based on your own shooting style and the subject matter you're shooting. Remember, not that long ago, folks were shooting shows with Hasselblad 2 1/4 film cameras and fixed focal length 80mm lenses. Wait a minute; most still do!!!! Makes you wonder doesn't it?
Continued good luck with the shows and congratulations on your work.
Jim
