Tori,
lots of folks think they can only rent cameras and lenses at a local store. Actually, the best places are online services like LensRentals.com or LensDepot.com. I've rented from both and both are excellent. They'll ship you the lens with packaging and label for return postage. And they both provide superb customer service along with insurance in case you damage the lens during rental.

In the case of LensDepot.com, they also rent lighting so you could try out some of the equipment you're hearing about. I recently rented their Vagabond II for a show where I couldn't get to the AC and it worked great with my Bees.

Bob's advice is good. I've never found the 400s inadequate but for the price difference the 800s are probably a better deal. And if you can find the budget for a Vagabond, do it. It's great for places where you can't reach AC or outdoor shooting with your strobes or just overall control of every lighting situation without having to run long extension cords.

As for a backup camera body, yes, it's a great investment. If your current lens is giving you decent image quality, the best next investment, IMHO, is a backup body. In fact, if you can upgrade and keep your existing body as a backup, that would be even better. Prices for used semi-pro bodies like the 30D and 40D are very competitive right now. As are refurbished bodies from Adorama. Check them out at www.adorama.com/catalog.tpl?op=searchresults&searchinfo=Refurbished By Canon.

Don't overlook used lenses or bodies. Lots of people like to upgrade frequently and what they are getting rid of may make a perfect addition to your camera bag. Places like Adorama, B&H and KEH offer great selections of used equipment and, in general, it's in excellent condition.

We all work on limited budgets . So we learn to stretch our $$$ whenever possible.

Jim