You could look into the various nano species that are appearing more and more in the hobby. With a 100 gallon tank, you could have VERY large schools and get to see how they interact when there's more than just the minimum 5-7. Then you can round it out with some other smaller, but not nano-sized, fish for additional variety. Just make sure that the other fish aren't big enough to eat the smaller fish.
As an example, I'm (slowly) putting together a planted 45 gallon and am planning on a school of 40ish Ember Tetras.
Or, if that's not your thing, then maybe a "semi aggressive" tank with a large school of Tiger Barbs and a few Red Tail Sharks for the mid to bottom area. With a 100 gallon footprint, there should be plenty of territory. You might even try an Asian Bumblebee Catfish, which are normally thought to be too large and aggressive for the average community aquarium.
BTW: that thing about corys and gravel is a bit of a persistent myth. People who have actually done research and experiments on the subject found that issues with barbels are more likely the result of poor water quality (ie high nitrate) rather than the substrate itself. If you don't want Corys, that's fine. I just didn't want you to think that you CANT have them because of the gravel.
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