Good luck finding an answer. I am very new also and setting up my first tank. The standard answer is always as big as you can when it comes to sump and refugium questions. As far as layout of your sump and refugium you can read about a hundred different ways to do it and people can make great arguments for every one. I finally just picked one that made the most sense to me and that's what I'm going with. Oh, and let's not leave out the people that say that a fuge is not that beneficial either because they have good arguments as well. From what I've found is that there are many ways to do your set up and you just have to roll with what you feel best with and adjust to what ends up working for you. My sump I am building is from a 30g tank which is 36 long and 11 3/4" wide inside the tank. The drain/skimmer area is 10"x10" tall, then bubble trap which is almost 3", then 10" for the return, the next baffle is 13" tall so that makes the fuge area about 13"x13"x 11 3/4". I will tee off the return and put a valve to the fuge that way I can adjust the flow to it. I went through many combinations on my mind before this finally made the most sense. I stole this image from a guy on another forum but, this is how my drain and sump set up will be. My display is also a 75g.