^^ In truth, LeaoLouro, I don't believe there is a limit... even the whole universe.

I think Him already sort of mentioned this, but in a dream the entire universe is "You," period; there are no other objects, only other aspects of your own imagination. So, if you can come to fully understand that there is no separation between DC "You" and the other people, things, critters, landscapes, biospheres, etc., then there is no reason you couldn't become any or all of these things -- because you will know that you already are them.

Though it would be a very difficult exercise, because our natural state of dualism (a "me" separate from and observing everything else) works all too well in dreams, I think it is an exercise worth attempting and perhaps working on for quite some time. This is because it will help you to develop a sense of non-dualism, an achievement that ought to be a standard goal for all LD'ers. If you want to get started in this (and haven't already) I suggest you look into sleep yoga, because this is a major focus of that discipline.

Finally, just to echo what others have said, be advised that, as far as I know, even after you've developed a purely non-dual perspective, the other objects you might occupy in your dream will still be extensions of you, so you will not learn anything more by being them, except perhaps how powerful your imagination can be... unless of course there really is an actual dream plane that we visit every night or dream-sharing is possible, in which case you might just happen to find yourself experiencing life in an actual ant colony, which would be very cool, but I don't think that's what we're talking about here!