that sounds good! I think the guy from "foo the flowerhorn" uses one of those. Im sure my dad would be very excited to help me with a project, and it would keep me entertained during the winter! i think ive even seen premade ones sold on amazon
Yes the ones I've seen on Amazon are quite small but perhaps there are others I haven't seen.
My most successful design with this was a 3' planter box i drilled and filled with bio rings and pothos. It worked well but it was rather noisy, needed fine tuning for sure:

Here is another similar example I found on Google where a keeper mounted it on a wall shelf. I think theirs looks better!

If I had it to do over again I would use a sponge pre-filter on the pump inside the tank and drill the bottom of the planter for the drain, perhaps use a durso style standpipe to make the flow more quiet.