55” x 19” x 19” begins!

[Joe Reefer]

My thoughts for flow was to rely on the CL for circulation, the flow to the sump really is only to feed the skimmer, heaters and some mechanical filtration.

I second that. Flow through sumps should be kept to a minimum so you don't end up with a micro bubble problems later. That being said you may be able to reduce the size of your overflow pipe. I can't find it now but there was a thread on RC of a similar tank to what your planning.