Looking for feedback on return flow

[lastlight]

Hello,

I'm new here and planning my first aquarium. I'm having this custom built here in Calgary. I'm looking for last-minute opinions on this plan before I start the build...tomorrow likely.

http://www.thelastlight.net/temp/tank.jpg

Pretty basic here. I want to avoid powerheads:

- 18" wide overflow spanning entire width
- 2 x 1.5" drains (Made an educated guess as to their size)
- Return through another 1.5" hole
- Return splits to 4 loc-lines. Intend to aim the 2 near the overflow towards the opposite end/ middle of the tank. Other two to maybe aim a bit downwards, against glass maybe.

My questions:

Will my holes be large enough?

I'm going to be buying a Quiet One 3000 or 4000. 780 / 1017 gph respectively. Which is my best bet, considering head loss, and restriction of loc-line?

I intend to keep softies and maybe some lps initially. perhaps try sps at a later date.

Thanks for any and all feedback!

Brett