newbie piping questions - what size return - what size overflow?

[Milad]

So im going to be buying a 180g in the next week and a half.
I decided to model so I can get a feel of what its going to look like in my place.
Here is what I have so far:

Green is return, red is overflow



refugium pluming


a shot of the back


The final product



As you can see, I want to get a little baby refugium on display just for shits and giggles.
So my questions are:
What size piping should get returned from pump?
What size piping should T off to the refugium and back into sump?
Is the return and overflow too close together on the refugium?
Is the return and overflow too close together on the main tank?
What size piping should be on the main tank overflows?

Any help is greatly appericated, im new to these boards!