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

[Milad]

to answer some questions
I dont have overflow yet
And only two holes drilled around 8in from top 4 inches from side (i dont have aquarium yet so im not sure exact mesurements)

You guys are giving me some great info btw, very appericated
Taking into considertion everything everyone is saying, I made two new models. One has a herbie one has a bean. Both returns feed to other side of tank (now i gota build a damn canopy!)

1in drains, 3/4 return to 1/2 at the end of return (the T for two nozzles).
At the ends of the return, ill drill two holes on each end so it doesn create a siphon when water gets below them.

My biggest concern about the herbie is it looks like I have to try to match the flow of the return pump with the full siphon otherwise its going to make some noise. Plus there is only one emergency which kinda freaks me out.

For the bean, because my holes are so low, I had to "modify" the design by going up then coming back down. Not sure if thats safe or not.

I didnt model the refugium in because it looks like I have to do a herbie/bean to the small 5.5g otherwise all the fail safes im doing on the big tank wont matter if the 5.5g drain clogs. Thoughts? I really wanted a refugium display!

Here is the herbie


Here is the bean