From what i gather there has to be a union from the overflow box to the pipe going into the pump at some point.
Now as for the return pipe to the aquarium from the sump should i do one or two on each side? and does pipe size matter as much in this case?
Also, what kind of return should i go with, spray bar, nozzle, etc?
I know i sound like a complete noob but i just want to get all these questions out of the way and do everything the right way because if i did run into a huge disaster my wife would never let me live it down lol
You can do whatever you like for returns. It is really up to preference as long as it is water tight and meant to handle light pressure. I prefer Loc-Line. It is 3/4" which is a common and easy size in PVC to work with, cheap too. If you go this route you can reuse them on future builds. I have a box full at this point (plumbing one tonight actually)...
The returns from the pump (make sure there is a union here) back up to the tank can be one larger line, two smaller lines or my favorite, 1.5" line stepped down at the tank wall to 3/4" with Loc-Line in the main display.
The PVC diameter is important here. Anything small restricts flow. I prefer 1.5" plubming for as much as possible with Reeflo pumps. Then stepped down to the return. With a Reeflo you can add a few extra restrictions without the same loss as some lesser pump models.
Some examples for you of a simple return. I can go through the back wall of the tank (my preference) so this is the next best alternative.