Horn shark gets too big IMHO for 4ft.... I had an 8x6 and it was on the bottom end of sizing. Granted my horn was 24"+ but you want to keep something that is 2.5x the animals length for the sides.
Marbled or banded would be ok and maybe 1 small round ray depending on the amount of rock work as well. I wouldn't go for a smoothhound as they are quite active and would be doing small repetitive circles all day.