Glad to see you jump in here!
Pink Tail is(are) definitely going in there.
In the past, I have liked Heckelii, even before the biotope so I kind of considered them but their preferred water temperature is a lot higher. Other than that, size and temperament would have been ideal IMO.
Oscars... I'm trying to steer clear off them but who knows.
I have forgotten about the pike cichlids. I have looked into them before, including the red wolf fish, but aren't their mouth size a concern as well? IMO, it would just be like having a red terror but in another form. The chances of aggression being less would be better on the festae's side is what I think.
Apistos look great, the least I could do is put one in there and see what happens. The elongated body of the Apisto might push it towards the feeder side though. In this case, I think the worse that could happen is the GT would refuse pellets and aim for live fish if he gets accustomed to it, hahaha. I've read someone say that in some cases, once they get a taste for it they'll take nothing else.
I appreciate all the info, I didn't even know about most of the fish you recommended! I'll definitely look into them more
P.S. Check out my setup videos
http://www.monsterfishkeepers.com/f...n-terrors-amp-fry-VIDEO&p=5889299#post5889299