New to Sumps

[locoyo386]

I have a question, I have never done a sump filtration, thus I have questions since I am venturing this route. I read that the bigger the better, well regarless of what size sump, is there a way to figure what flowrate you should have in the sump? I am trying to use my sump as a mechanichal filter and bio filter (no skimmer, or refugeum at the moment maybe later for the ref.). The reason that I ask is because every type of filter pad I place in the sump restricts my flowrate quite a bit and that leads to a low level of water in the return pump chamber. Any help or ideas would be greatly appreciated thanks.