If I were you I would put the fuge first, then the skimmer and then the return. The fuge part needs to be as deep as you can get it for maximum effectiveness. The middle section with the skimmer depends completely on your model of skimmer. If it is an in sump skimmer then the depth of that chamber depends solely on where your skimmer likes to operate. I have a Kent TE skimmer and it likes a depth of about 5 inches. Last, I would make the last chamber (if you really need one which I don't think you do) as deep as the pump and just a little deeper.
I would put the fuge first because it HAS to be deep. Water only flows downhill and so you will have to put it first, followed by a shallower skimmer section and then and even shallower pump section.