[Deep Blue Sea]

I am in the process of trying to build a sump for my 72 gallon bow front reef. The sump is 29 1/2 X 11 3/4 X 17 1/2 which are all the inside dimensions. I have the baffle glass all cut and those are 11 3/4 X 14 1/8, the extra 1/8 was a mistake on the first cut and was only supposed to be 14" but I allowed for the space between the head of the glass cutter and the actual cutting wheel in the wrong direction and ended up with the extra so I just followed this on the next cuts for continuity. I am planning a linear design and it will be intake, refugium, return. I have a return pump and it is a mag drive 9.5 and I plan to run some kind of an overflow box with the lifereef brand being my choice, but it is getting hard to come by due to shipping charges mostly. To drill is not an option just now since I cannot move it to drill, but on my first opportunity I will drill. The two main concerns and questions I have before I proceed any further are, is 3 3/8 inches of head space enough for overflow, and what size would you recommend for each chamber. I do have a skimmer, but it's a H.O.B. Aqua C Remora Pro that I have with no immediate plans of replacing because it's relatively new and not an expense I can justify right now and especially with the war department (A.K.A. wife) I am thinking that the most important chamber might be my refugium, am I correct? My thoughts were 8 inches for each the intake and return and the remainder of 10 3/4 after the bubble trap is added and you factor in the thickness of the four pieces of glass which is 3/16 thick. I don't know why I came up with these dimensions, other than they seemed to make sense with the little I did know about sump/refugium builds, which is extremely restricted. I welcome any advice or input and will be very grateful for the time you give me for this build.