Hey, welcome to the forum!
I think as long as you give your frogs plenty of space and the right enviroment, there's nothing wrong with wild-caught, so long as they're legal to collect and in good numbers in your area. Even captive-breds are not tame like dogs are and behave not much different to the wild ones, however the benefits of captive bred are that they are relitively free of disease but as long as you provide the proper conditions and treat them if neccessary, it should be fine. It's best avoided purchasing WC from pet shops though, due to the stress they go through with transportation. A 20-gallon tank is a good size to start with and everything sounds good. Make sure to get a thermometer and hygromter to check temps and humidity, though. It would be good to get a book or two, if you haven't already just as they provide good in-depth information. There are many books available that feature their care under the same as recommended for green tree frogs.
Jason