Hi, you have a syrian, very cute.
As he is a syrian he will need a bigger wheel, 11-12 inches, which is maybe why he isn't using his current wheel. It could be uncomfortable for him as it isn't big enough. You need one big enough so his back doesn't arch when running.
I'm not sure how big the cage is, so if there isn't room enough for a correct sized wheel you may need to upgrade the cage as well.
As he is a syrian I am confident in saying the nipping was like I thought, he is just working out what/who you are. If you see signs of him doing it again, just move your hands out the way. He will soon learn. try giving him pieces of food through the bars, then move to the hand inside his cage.
You said he has a playpen, when you feel ready, you could try transferring him to it in a mug etc like I said before and if there is room for one of you to get in with him, that is a good, safe way for him to get used to you. They normally end up using you as a big climbing frame at some point. This is also a good time for him to get used to your hands, you can try and let him climb up on to them, and let him walk from one hand to the other, as he keeps moving, you keep putting your free hand in front of the one he is on, I would build that up to 10 times then let him run free again.
Another thing to try is make your hand into a fist so he can't get your fingers, and just place that in his cage or the run, if he looks like he is going to bite, move it out the way, otherwise let him explore you.
I think these videos may help with what I am trying to explain.
https://www.youtube.com/watch?v=0XnW...m&index=5&t=0s
https://www.youtube.com/watch?v=rCAM...m&index=6&t=0s
Hope this helps.