Nice setup!
I'm not sure about the humidity, but I am 100% certain someone else here will give you advice on that. If you want, I can contact some of the experts on here to give you a bit of advice too.
Yes, that's an American Green Tree frog (Hyla Cinerea.) They make very fun and interesting pets.
Make sure any crickets you give him are smaller than the space between his eyes. For tree frogs, I'd recommend dusting the crickets 1x a week with both a Calcium mix, and a Multi-vitamin mix. You can buy both of these products at your average petstore in the Reptiles section. In case you don't know how to dust, it's very simple: Place the crickets in a bag, place a pinch of the dusting mix in with them, seal the top of the bag, shake the bag until the crickets are either fully or partially coated in the dusting mix, and then simply place the crickets in the enclosure.
Also, I must strongly enforce this, but be VERY careful about closing the lid of the tank at every feeding/handling/cleaning/etc. These guys are master escape artists, and believe me, having a runaway frog is not fun.
I do recommend putting the wallpaper on the sides as well for the first few months, because it helps lessen stress in frogs, and makes them feel more secure. You may want to pick up a cheap humidity tester or Hygrometer for the tank, as well as a thermometer. Otherwise, your setup is perfect.
Oh, and Welcome to the Frog Forum

!