Tilapia is good. Big pellets is good. Tilapia stuffed with pellets is good. Juvenile is a broad word, but either way getting him off live asap is a good thing.
Shrimp and other white fish is good. As stated before shrimp only went be the best, but it definitely won't hurt from time to time.
I use to feed mine mostly tilapia and would stuff the pieces from time to time. At least it made me feel like he was getting a well balanced diet