I still dont understand how Nunu jungle even works. I mean, yeah you have good sustain, but thats pretty much it. It takes ages to clear, and your ganks are so...meh. --- "So selfish them" would be their cry. And, who'd be brave to argue? Doin' what you people need is never on the menu!
Nasus is easier than Hecarim for a beginner but I would recommend Xin instead. He falls into the same category and if you fail with Xin consistently just stop playing. --- ~Victory needs no explanation; defeat allows none.~
Nunu jungles clear is fine, it's not the fastest but it's not slow either. He slows the enemy in lane over and over until your laner can kill them. Speed up your laner, slow the enemy, and ulti for the big damage.
I think of him kind of like a Maokai jungle but with permaslow rather than a snare.
As for learning, I learned with Shyvana, but that was S2. Skarner is a great suggestion for learning to jungle, since if you can get close enough you can provide all the CC/Permaslow to make it a successful gank, so you don't have to depend on your lane as much. --- Now these points of data make a beautiful line, and we're out of beta we're releasing on time! So I'm glad I got burned, think of all the things we learned!