Frog Prince isn’t too hard to knit -- he can be a little fiddly (especially if you make him on tiny needles), but I think that advanced beginners to intermediate knitters will have no problem; if he were on Knitty, I’d probably call him piquant.
If you can knit in the round on double pointed needles, increase and decrease, you’ve basically got it. There is a small amount of seaming involved, and at one point there is a picot bind-off (if you’ve never done it before, don’t worry -- it’s very easy, and I try to explain it step by step. There are also some great resources on the web that can walk you through it). It’s pretty easy, and pretty quick.
As this is a toy, there really is no right or wrong gauge. I have knit it on 0s with lace weight, and on 8s with bulky yarn, which makes this little guy a great stash buster!