180 gal build. Long time in the making

So I'm going to start my stand tomorrow after work. Using 2*2*1/4 inch stainless steel Angle iron. Gonna make it 30 inches tall so I can still reach the bottom of the DT when full. As far as the sump I was thinking a 55 gal wld b good but have room for a 75 if that is better. Any suggestions on a mid range protein skimmer? If I need to spend the extra money on a better skimmer I will. I'm under the assumption it's almost like the heart of the system.......



Any suggestions are greatly appreciated.