Need help with my 120 gallon upgrade

Hey guys, I just bought a 120 gallon reef tank 48"x24"x24" with one overflow box on the left hand side. I don't know the technical stuff but someone on 3reef should. I basically need help calculating the flow rate of water per pipe size and which type of pumps do I need or should use. I plan to build a wall around the tank with sheetrock to make it like a flush mount. There will be a sump. I want the pumps to be in-line not submersed in the sump. PVC plumbing with shut-off ball valves but I don't know what size pipe I should use for my drain and return pipes. please help... Any suggestions will be greatly appreciated.. thank you

 

I use an ehiem 1262 and it had just the right amount of flow full open as to not overwhelm the overflow. The return for th ehiem goes through a 1/2" seaswirl. The other step i took was to use a reefflo dart plumbed to an ocean motions 4 way. All using 1" pipe that comes in 4 different areas in the tank that is then split by Y's at each outlet, the intake for the pump is 4" and is placed toward the bottom corner of the tank, hidden behind rock work. Hope that helps you some. I also added a tunze and a korallia for a bit more flow in the center of the tank