Okay so, your filters are fine no upgrading needed.
Having a pump/ power head isnt bad id just turn it down and keep it away from the bottom ive noticed my senegal is more active with less flow.
Best substrate is sand. Its safer for the bichir and easy to clean and it looks good.
One male and a female will fit and get along in the tank. You could probably do more if wanted. No the polys will not breed readily.
Mine love drift wood, live plants and rock formations.
If you have any other questions just ask
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