WoW!! Very impressive for your collection and pictures (first time to be strobist!!)
You don't have to buy PW, overpriced. Cactus is enough for you. I never use Canon proudct before but I know 430 is the classic of classic. 580 is even better?
I will try to finish my blog sooner, (DIY and Restricting light). For small subject, you need DIY Snoot and Grid. Or don't aim to stones directly but probably aim to a white paper (above the stones with some angles) first and then bounce it to stones.
What's under the stone? Seems too reflective.