I don't know enough (still learning) to offer filter advice but I am running a 2400 litre per hour pump through the sump for my 1500 x 60 x 60 tank
(450l). I do water changes 25-30% once or twice a week depending on the time I have available. My discus (6) are around the 10cm+ mark.
also 9 cories, 4 bn and 4 sae.
The best advice I was probably given was not to feed heart as it would make it too hard to clean the tank properly. I feed blood worms and pellets instead.
They are happy, healthy and growing.
Look around and see if you can visit others with these fish, look at their setups, ask heaps of questions and then decide what you think is right.