Welcome to the Frog Forum!
Good work so far! I'm glad that you rescued that poor little guy! But, here's a few tips and suggestions for you in terms of his setup:
First off, I would buy an aquarium wallpaper from a petstore big enough for the back wall and sides, and either tape it or use warm water to attach it to the sides and back. Preferably, one that matches his natural environment (Ex: a forest wallpaper). These help reduce stress, and make your frog feel more secure. Another thing I strongly suggest is that you switch the substrate you have right now for Coconut Fiber, also known as Plantation soil. It's a safe, clean substrate to use. Bark, or similar substrates aren't safe to use with frogs because if they accidentally ingest some of it it can cause internal injury and/or impaction, which is the blocking of the intestines.
I also strongly recommend picking up a small container of Reptile Calcium + Vitamin D3 powder and Multi-Vitamin Powder. These give your frog the Calcium and Vitamins it needs. You can lightly dust the crickets once a week with each (though on separate days for each of them.) To dust the crickets, simply place a pinch of the powder in a bag, drop the crickets in, seal the bag, shake it around, and then place the crickets in the tank. Your frog should do the rest of the work. Oh, and make sure the crickets are only about the size of the space between your frogs eyes. Any bigger and it may be too much for him/her and she/he may choke on it.
Another thing I recommend you pick up is a humidity gauge, or a hygrometer. These can also be found in petstores, and they will tell you the current humidity of the tank, which is important as Green Tree frogs typically need a certain humidity level.
The Reverse Osmosis water should work, but I personally think picking up a Water Conditioner such as Exo Terra's Aquatize is the best option. It can last you months, and every bottle can condition about 400-500 liters of tap water. Simply follow the instructions on the bottle/package and you'll be good to go.
I don't know much about misting and humidity, but there are lots of people on here who do, and I'm sure they'll comment on this thread and fill you in.
Good work so far! Keep us posted