best flow for refugium?

Sounds like you're wanting 2 different things! A SUMP stores the water, adds good volume, and can store lots of equipment, and the water flow can be fast. A refugium is supposed to be a safe place for lots of little organisms to grow, and should have slow water movement. You can use one tank with mutiple compartments, but you'll want to have one area with fast movement (ie, water comes in, and most of it goes back out, while some trickles through a smaller section). It's do-able, you'll just have to play with pumps and setting up the compartments so you have good flow through the sump area, and slower in the fuge section.