I would want to maximize the size for the sump. When the cabinet is for a 5' tank then I think I can have a 4' to 4 half feet sump.
I think the main issue is to find the tank that comes with the cabinet from a single supplier so that the cabinet and tank fit perfectly. About the sump it can be bought later and it can be customize made and follow anyone design that can accommodate a return pump, skimmer and refugium.
As for lighting it is going to cost more as TC said. I am not sure. I have little knowledge about lightings. There are so many types to choose from. When I know little I cannot choose. There are LED
, halogen, fluorescent tube, LED
fluorescent, etc. Got to look at long term running cost as well. Its durability, electricity consumption, efficiency and deterioration vs time and worst of all the made, brands. Anyway, just got to blindly buy some and experience it? Pay to learn? or you can help me some?