I really like the combination of angels with tetras and cories. I had a tank set up with that before they got moved to my big tank and it was my favorite tank

I would go with the following:
3 Angels= 18 inches
6 Tetras (type 1)= 12 inches
6 Tetras (type 2)= 12 inches
6 Panda cories= 12 inches
54 inches of fish total
I would pick from the following types of tetras (they are some of my favs):
Cardinal Tetras, Gold Tetras, Black Neon Tetras, Rummynose Tetras, Lemon Tetras, Diamond Tetras
The only type of tetra you cannot put with angels is neons because they don't get big enough and will be eaten by the angels.