Progress on new pool build!

Finally!

I'm currently building a small pool on an island in Panama. Dimensions are 14’ x 8’ x 4’. Of the 14’ in length, 4ft will be 1ft deep and the remaining 10ft will be 4ft deep. Basically a shallow end to sit in without being fully submerged. It will be all poured concrete, hand/shovel mixed on site as there's no way to get a mixer to where I am unfortunately. It's daunting but the plan is to mix on Friday.

I have a few noob questions regarding plumbing before we pour. There will be 2 main drains that will run out to the pump, a skimmer and then 2 returns coming back into the pool. First question, the skimmer has two ports at the bottom. Obviously one will also go to the pump (connected via a 3-way valve with the main drains), but the second port...what should that be used for? Vacuuming? If so, I'll run the line out, but will that also connect in to the pump somehow? I'm a little confused on how that should work.

Second. Returns. Right now I'm aiming to put them into the "width side" of the wall (the 8ft side in the rectangle) where the shallow part is. In my head they'll be able to return the water along the full length of the pool over to the opposite side where the skimmer will be, flowing over the shallow end to the deeper end, thus making good circulation. Does that seem right? Also, approximately how far down into the pool should the returns go? I assume as long as they are submersed it doesn't matter too much?

Thanks in advance for any help and I'll be sure to keep everyone posted on how it's going!
Ryan