If you could get decent sized ones, I'd go for a school of banner fish..... there are several types, but the "schooling banner fish" is obvisouly the most likely to school......
Heniochus diphreutes is the proper name for them.
Most tangs do nto actually "school" up in a home aquarium, unless you have 1000's of gallons and a couple of BIG fish to encourage them to do it.
The butterfly recommendation is of course assuming that your water quality is reasonable and you don't have anything "mean" that will bully them, like big triggers or nasty tangs.......
In a 375 gallon tank, I'd probably go for 5...... I am assumign the tank is 96"x30"x30". I am not sure how big they get...... I am guessing about 6"...... not quite as big as the common bannerfish I don't think.
Other options - how about a trio of Falcula Butterflies (Chaetodon falcula)?
It really depends on what you have got in the tank already?