Heres a head loss calculator-

Captive Reefs - Head Loss Calculator


and a drain/overflow calculator-

Captive Reefs - Drain & Overflow Calculator


These will help alot.

I see that under 1000 gph is a good max for a sump, for the skimmer to do its job, but I am wondering what minimum GPH most recomend for flow through GPH should go through the sump.

What are the drawbacks/advantages to a faster or slower flow rate through a refuge?