If you choose your mechanical media so that it is easy to clean and you clean it often you should be able to remove a good majority of the debris before it has a chance to break down to nitrates.
A 55g with filter bags or filter foam should do the job nicely if you arrange them so they are easy to get to and remove to clean. Fill the rest of the 55 with pot scrubbies or any kind of bags of bio media set on top of several large air stones and this should give you enough living space for all the beneficial bacteria you will ever need.
You really don't need a huge sump if you clean it often... which in my case means that it needs to be easy to clean. Good discipline in doing scheduled water changes will be your best way to keep your fish healthy and happy. Any filter, no matter how big, is not a substitute for regular water changes.