Maelv,
There are alot of ways you could set your sump system up. Give me your email and I can send you some pics of how I have my setup. But either way, your ideas will work. I have found out that putting your skimmer after your refugium is a bad Idea. I would put your skimmer before your Refugium. So chamber 1 would be skimmer, chamber 2 would be refugium and chamber 3 would be return pump tee'd off back to tank and the refug.
As far as Papijames, Give me your email and I can show you a way to build a 45g sump/refug for about $50 or less.
29g Biocube w/ Intermediate Lighting.
75g RR Tank w/ custome 3 1/2 ft stand and Custom sump setup
14g Bio Cube
46g Bowfront Freshwater
30g Gold Fish cube