You could, just make sure you have enough filtration for those big bioload fish. I think that would be all you could put in there though, with the exception of a few bottom feeders. How about some 4 line pictus cats? I have 2 and I love them.
Of course your welcome. One more thing, really pay attention to the temperments. I have had oscars be mean and then have them where they ignore everybody else and only wait for food. Just get all those guys early on and they should be okay, but Im pretty sure you already know that.
One GT, one Jag and one Oscar would look nice. Keep your hard-scape to rocks and driftwood since they'll be digging and moving things around as they see fit.
What ever you decide to get, putting them in together while young should allow them to grow up together without any problems, but you never know for sure. The temperament and personality can vary within a species. Just keep an eye on them for any territorial disputes and good luck!