You can't use a wheelbarrow to move material? That's how I move most material. But I've done the bucket procedure too. It's certainly work, but doable. Good work out. Like I said, I wouldn't buy the manufactured systems either. Just cheaper and easier to built it myself. I like doing this type of work. The main issue I think you would have is the speed at which water could flow between rocks for such a high GPH. 2" drain rock and a 5 gal bucket is OK for say 2000 or 3000 GPH. Of course you could just use 3 or 4 pumps. What I would do for a single 10,800 GPH pump is dig the basin and lay EPDM liner. Then a 2" thick floor of concrete, no steel, over the liner. You can get a little fancy and form a trench for the pumps if you like. Dig a V type bottom before laying the liner. Then final form with concrete. Then I would dry stack concrete block to form open areas. I'd cover with 1/2" Hardie board. JamesHardie sells in the Netherlands but there are no doubt other sellers of cement board in your area. The blocks are stacked so the board on top doesn't have to span more than say 6-8". The board is not rated to span any distance, but I find it OK for 6-8" spans for occasional walking. Certainly OK for holding up even 6" deep layer of stone. When I back fill I place rocks large enough to block gaps between blocks, and then smaller and small stone until I get to the top of the blocks. Then the cement board and then cover with the final layer of stone. You don't have to cut holes in the cement board, should be plenty of gaps around the edge. I do cut a small piece of cement board to cover the pump or pump intake so that's easier to get at. That should get you 500 gals of water easy which should be way more than needed. You can install 2 or 3 submersible pumps instead of one external to get the amount of water you want. Getting the sound of a waterfall the way you want it can be tricky. Many people do want Niagara falls. And they love it when it's turned on. But about 2 minutes later they realize they can't hear anyone talking unless they shout in their ear. Then they realize they can't turn down the flow and are not happy. Not saying this will be true for you, but it happens a lot. And there are different moods you may want. Sometimes a tiny bit of noise, other times a lot. Multiple pumps can provide that. And three 4000 GPH submersibles can be cheaper than a single external to buy and run. The biggest factor to me is pump noise. I've read many times in forums where people said their external pump was quiet, and they can be. But a water feature in a small space the last thing I want to hear when I turn it on is the customer say "what's that hum?" I don't want them to hear anything other than water. Also a super cool piece of equipment is a remote control switch. These are only $10-20, plug into an outlet and then the pump plugs into that and you turn it on and off with a little remote. Way better than having to plug cords in an out and even better than wall switches imo for the cool factor. You can also buy more complex controllers so the falls can switch on automatically just before you wake up in the morning or come home from work. They're kind of expensive, like $100-200.

That's pretty much how my bog works! Except because of the way we built ours, it's a challenge to get the water level below the gravel level, (waterfall is a little bit too high >.<). The bog water level is above the gravel in a few spots, and it becomes a string-algae-covered mess. But... I still love my bog =D Only thing is I wish it was bigger! Plants take off like nobody's business! We have a triple pond setup -- bog is at the top, then a waterlily/frog habitat, and then a small goldfish pond -- all told about 700 gallons. Note this year we will be expanding the lower pond, and our bog will likely be too small, but we have plans for a supplementary waterfall filter. Here's a photo from last year from our 2nd story deck. In the photo, bog is at the bottom, middle pond is top right and lower pond is top left. The pump sits in the lower pond, then tubing brings it around to the bog via perforated PVC and the water cascades down from there. We put in a check valve in the bog piping to keep backflow from occurring during a power outage, as well.

It doesn't have to be at the end, in the waterfall. That would ruin the effect, for me, and I'd choose a different option. Is there an overhang on one side? If not, the outlet could be in the cabinetry that faces out. Personally, I'd use plug mold underneath the stone on the kitchen side. Or, a pop up outlet in the countertop.

Have you considered bringing the bar top down to counter height? That would be my preference. If you have quartzite to use as a backsplash and want to do so, go for it.