Wildlife Rehabilitation laws differ from place to place, and you would need to get in touch with the Game Warden (or other government agency pertaining to animals where you live) to find out just what you would need to do.
I was a licensed rehabber in KY and was required to have sturdy cages in my yard, inform my neighbors of my intentions, and a game warden came to the house to talk to us and inspect the cages we had. (One year for Mother's Day my daughter & her husband used the frame from a big wooden swingset and made me a big raccoon cage.) I had a smaller cage that was up on legs so that I could reach into it easily with a door in the front and a double panel at the back so that whatever I had in there could have more shelter and privacy and it made it a lot easier to clean the cage. I raised both a deer and a flock of Canada geese in a chain link dog pen - but not at the same time. I don't know if you live alone or with parents or with a significant other, but you need to talk to them too, because this turns into an experience for the whole family if you have more than one or two animals.
You will also need to find a veterinarian who will be willing to help you in case of illness, surgeries, etc. As a rehabber, a lot of the animals that come to you will be sick or injured. Sometimes the Mom will even kick them out of the nest if she senses that there is something wrong with them. If you are lucky you will get donations from people who bring animals to you. Otherwise, be prepared to absorb the cost of all food, bedding, cages, etc.
After you get all that done, print you up some business cards and take them to all the clinics (especially ER's) and wait for the fun to begin!! As you learned with Puppy, it is a very rewarding thing to do and you have to go in realizing that these are
WILD animals and must someday be returned to their natural habitat. They usually let you know when it is time.
Good luck! And let me know how it goes - I'll be glad to answer questions regarding feeding, etc., on any other critters you might take in.
Crittercall