Plans for my first build

[Kevotron]

I am starting my 40G Breeder project SPS dominated
This will be my first time im building things such as "overflow, sump, plumbing etc" by myself so i guess i am all new to this..
I want my overflow box as less space consuming as possible, I don't know what size hole to drill etc... only thing i know is my sump is 15G ... location/size of baffles has yet to be determined.
I was wonder if yall experienced reefers can help me in designing this