airborne101,
Use a skimmer to remove surface debris. Definitely split the drains.
Make sure the structure is sound. These long, narrow water features can move easily and crack.
Bubblers can act as returns. It depends on the intended useage.
Floor returns for cleaning? Good luck.

In my neck of the woods the guniters will clobber you on the price to shoot a monolithic concrete shell. They have a minimum and this shell would come in at 2500 just for their service alone.
I'd build this platform with two sided forms laying the bottom of the inside form of the wall 6" above the dirt. Have the excavator dig a footer beam all the way around the perimeter 6 to 12" deeper and place some footer beams across the short side on your 6,12,18,24. Place the outside form first, tie steel on a tight schedule, 4each #4 boxed beam and walls/floor #3 8"oc, then form the inside wall. Call a concrete company and order 3500psi redimix with the smallest aggregate they offer, I'd ask if they have 3/8" sifted.
I'd guess at about 6 to 7 yards of redimix concrete, my cost would be about 500 to 600 for the crete.
I'd hate to guess the subcontractor costs in your area and would suggest taking quotes from an excavator/formsetter, rebar contractor, plumber, electrician, and a brick/tile mason.
One pair of VGB compliant main drains and a surface skimmer are a must, the bubblers can act as the sole return but I'd also suggest a wall return to aim flow at the skimmer. "A" profile floor returns will do so so for keeping the floor semi clean. You could also use an old style 5 port water valve from Polaris in conjunction with a Leaftrapper, it'll act much better as a debris catcher better than the skimmer. You'll need to utilize spa lamps for the reduced lumens due to your small size, large lamps will fit in 12" of water but offer way to much light.
For a hands on contractor, this type of job has the potential to hit a home run, but farming it out to all the different subcontractors will get expensive due to the minimum charges from the subs.

I hope this helps.

See ya,
Kelly

Thanks guys so much, want to get back to the designer asap. He is interior design and is open to suggestions. First, the budget for project is way too low as we are doing 2 shade structures, stamped concrete, paver patio with fireplace etc. We don't do pools,but would lay piping for future add on. Frankly DH can do concrete, rebar, stone, tile etc, just the water aspect is beyond his license. Second, we aren't thrilled about the design, its not functional at all, just pretty when viewed from inside. And he wants to do this at grade, we think raised is much better as they could sit along the edge, thanks Kelly for that info. We do work around 2 pool companies who could do the install totally, but again that budget is way too low. Personally I would go whole pool in Vegas, no brainer. Will keep you posted, should be a nice project if we can get it on our terms. Thanks again, Barb

Here's what I've told EVERY designer who's worked for me over the years.

quote" we aren't thrilled about the design, its not functional at all, "quote
It doesn't matter how you feel about what they want, they're paying for it, and if you don't design it the way they want it, they'll sign with another contractor who will do it their way.

quote" just pretty when viewed from inside. "quote
I'm certain that this is why they want it this way.

Honestly, I'd prefer to have a feature like this at my home at deck grade, it's a clean seemless look when viewing it out the window. These would be wicked beautiful if they dumped the 5 lights and use 5 Crystal Fountains fiber illuminated foam jets, all you'd need to do is place some round perches for them at 3 to 5 inches of water depth.

I'm not trying to knock your design logic, it's just my .02

Good luck on the capture, hopefully they'll come to their senses on an unrealistically low budget.
I've encountered this so many times over the past 18 month's it seems like I'm reliving the late 80's recession all over again.

See ya,
Kelly

Here is a link that might be useful: crystal fountains website

Kelly, thanks for the advice, you are right, its what they want. I'm much more opinionated than DH. At grade would give the desired look. Its not the water feature thats not functional, so subtle changes mid-build on the rest of the project can be done. Also really appreciate the link to crystal fountains, awesome idea. Budget, we will see. Will keep you posted, big thanks, Barb