An AquaClear 50 is rated for "up to 50 gallons", so that would be more than enough filtering capability. You figure at 200 gal/hr, and with 7.5 gal. capacity, you would cycle that whole tank nearly 27 times each hour.
Is that too much? Is there such a thing as too much filtration? I don't believe so, but you could probably save some money by purchasing a smaller filter.
Maybe someone with more experience has more input, but I think you'd be fine with that filter. Then, if someday you upgrade, you could still use that filter in a larger tank.
As an after thought, being that the tank is only going to be half full, the "waterfall" is going to be fairly loud. That's something to consider in a HOB filter type. Additionally, I'm not sure whether it would be good for the motor to have to draw water so far up the pickup tube. (When a tank is full, even though the tube picks up halfway through the depth of the tank, it has pressure from the water above helping.)
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