This really is a very pretty hat ... and the pattern itself is not difficult, I haven't done many intricate patterns before and even I had this pattern memorized after one or two repeats. :teehee:
As for knitting in the round ... It really isn't as difficult as it seems. It sounds like you've had a fair bit of experience with knitting flat, so I would definitely give it a try. I much prefer knitting in the round to having to seam things at the end! It's probably not necessary, but you could always do a small "test" project (such as the simple beanie you suggested) to practice the technique first. That way you could try out a couple of different methods of circular knitting to see which is most comfortable for you - for example, I favour the Magic Loop method for most of my circular knitting (less needles in the way and I only have DPNs in very small sizes) but I know there are lots of people here who hate Magic Loop and would much rather use DPNs.