Do not take this the wrong way and I am not trying to be mean but the questions you are asking are VERY basic and my first thoughts when reading your post was, this guy is in over his head getting that size tank and asking those type of questions.
But, I would say go for it, because you are going to be forced to learn allot. Good luck.
To answer your questions. And I am assuming when you say "overflow" you are referring to an internal overflow box.
Overflow position is more about preference and opinion and can have benefits depending on your final setup, so I do not have much of an answer without knowing more details about the tank and setup.
Are over flows needed for sumps? No, you just have to have a way for the water to get to the sump and back to the tank. Overflows are just one way of doing this. You could actually have the sump above the tank and have the sump overflow back into the tank.
Bulk heads are only used with sumps for the return right? You don't need a bulkhead on the sump, it depends on the return pump and how you choose to set up the system.
