Greetings all koi people.

Some of you would remember when asked for help and advice on my first pond about two years ago. The pond was only 10 000LT and got too small very quickly and the hobby grew immensely. So small that I decided to sell my house and buy bigger area for my newly planned pond.

But as us males are, did not really stick to the initially planned 40 000LT....and now I'm sitting with a huge 3 piece dam 95% finish. Tried to work the volume out to the best of my abilities and I came to 110 000LT pond??? (It is impossible to work out to the tee because of the shape. Once finish I will measure with a water meter for correct volume).
I never really planned to go that big and think I messed up a bit with my calculations and planning...hence I come for a second time humble to ask advise from the xperts

The 1st main dam is the last of three that still need to be marble lite. It is approx. 70 000LT and 2.8M deep It has two inlets and a bottom drain with a waterfall as a third inlet.

The 2nd 3rd together are approx. 40 000LT. Only one inlet and a bottom drain each.

My plan is to run two separate filter systems. 1st system run on dam1 and return all water back to dam1. 2nd system will run dam 2 and 3 and return .5 of the volume back to dam1 and .5 to dam 2and3.
This will create a overflow from dam 1 to dam2 and 3, giving me 3 waterfalls for oxygen.
Dam2 I want to set up as a natural filter system with pebbles, clay and plants. I also want to introduce crabs, shrimps etc, if possible.

Now for my questions and where I think I went wrong:

Are the outlets and inlets sufficient to handle the volume of water? I believe it is for dam 2 and 3 but not for dam 1, Alternatives? I don't want to cut into the concrete to add more outlets but would rather lay pipes now before I marble lite and then just marble lite over the pvc? Can I maybe run a pvc across the main dam and cut grooves into the pipe. This will ultimately give me two outlets with three inlets.

I don't have a settlement chamber because the pond is about two meters higher than where my filtration room is and scared that power outage would cause a massive overflow, loosing all 110 000LT water. This made me decide (help) it is better to go with a closed sand filter set up. Will two filters be sufficient with two pumps, bio and UV run separately or will it be better to separate the mechanical filtration with the bio filtration and UV separate?

I also haven't seen any bio filters that can handle this type of volume and might have to cluster the filters but that is going to cost quite a bit. Any way around this?

Will the natural bio filter/wetland in dam2 really contribute and how can I measure the success?

Will a sand and carbon canister (same used for RO water you buy) placed after the mechanical filtration not assist to take even the smallest particle out of the water? They come with automatic flush heads, no need to manually backwash?

So to wrap it up: Two separate filtrations for 3dams. Sand filter - Canister sand- Canister Carbon- UV light-Bio Filter.

I would appreciate all the help and advise I can get and try to upload photos to better illustrate.

Thank you.