No, mixing species is NOT a good idea.

There are a lot of reasons for not mixing species. For example; There are diseases that can spread between species, and what one frog is able to tolerate easily may kill another.

The skin secretions of one species of frog may cause harm to another species, even if the secretions cause humans no harm. Different species may vary in size so much that, sooner or later, one becomes lunch to the other; this can also happen within the same species if size differences are great.

Different species are different in behavior, some are more efficient, aggressive feeders than others and some are more active. All this can cause one species to become unhappy, or not get enough food and die.

For some scary examples of why it's bad to try and mix species, visit Mixing Disasters.

If you have a lot of experience keeping frogs and are ready to start setting up a natural vivarium then you can join the Naturalistic Vivarium mailing list at Yahoo Groups.