Lots of good ideas here! So tetras can eat fry all day and not be eating too much meat? I've used bettas in the past, but they always die of organ failure, and I'm pretty sure it's from eating too much meat/live gups.
Angelfish sounds pretty good, except for their eventual adult size, when they will eat all of the guppies...
Bumblebee gobies are brackish and that would be doable if there weren't a raphael catfish already in the tank to consider.
Some hardy tetras could be the answer. I haven't kept many small tetras, what kind are good and hardy? I'm a full-time student so I can't really put too much time into the fish right now, like I would normally for sensitive species.