4200 gal outside Tank/Pond Build (questions & advise)

hi. Renovating the garden and planning an outdoor tank.

About 14ft long, 8ft high water, 6ft deep.

I've drawn a rough sketch of what I want to do. Please add advise as well as help answer some questions.

Spec:

Material:
Structure will be reinforced rebar and a steel H beam frame, epoxied/tiled concrete walls, front glass viewing window.

Volumes:
Upper tank will be around 6ft long, 6ft deep, 2ft high and will be made of glass. Wooden deck covers filters and main tank. Filter area accessible via side.

Filter will be rougly 6ftx6ftx6ft

Inhabitants:
ATFs, Payara, Arrows, Dorados, other various in main tank. Gars or Koi in upper.

Temperature/environment:
Subtropical temperatures, will need heater in winter, area of tank in enclosed veranda with retractable shade.

Questions:
1. Filter element and number of chambers suggestions? I'm thinking mechanical jap mat in first chamber, then brushes in second and third.
2. Electric pump heater location suggestion?
3. Aeration location suggestion?
4. Will put in pumps for water flow in main tank. Pump placement + current flow suggestions?
5. Want to put in a skimmer. Thinking about a pipe that sits at an angle semi submerged at surface of water level but not sure if this will work given water equalization if drained back to filter.
6. Copying a Koi Breeder Farm design for drip bioball trough system. Bioballs are not fully submerged in water. The bioballs in the water fall resovoir would be however. Comments here?
7. Water pump requirements?
8. Best way to attach glass? Silicon to bare concrete, tile, Hbeam?

Thank you!

thanks for the responses.

there will be padded sheets under the wooden deck which create a walkway over the tank that should provide a level of temp insulation. In addition,the entire garden will be enclosed in a glass structure with retractable shade over area of the pond.

Gets to about 8-9C ambient for a week out of the year on non-sequential days. Winter lasts for 2-3 months, avg ambient in mid-low teens. Other than that the temps are around mid 20s-mid 30s Celcius for the rest of the year, semi tropical.

couple ideas I've been thinking about for the heat.
1) water heater as suggested above, i think some are made specifically for aquaria. was hoping not to have to go industrial with a spa heater. In my home, I use a single 300v tube heater and that's enough to keep the tank at 23C during the winter days. I don't have a heater for the house. During the rest of the year, it's so hot there's no need for heaters. Trick is keeping enough ventilation through the house to keep the temps down.

2) Heat the glass structure with an air heater. volume of space around 20Hx24Wx20D ft. Cost comparison... i have no idea where to start. This method is much simpler and i can enjoy it too!

skimmer:
if i understand correctly, will the following work, a pipe (90 degree perpendicular to floor) raised above water surface with perforations. plumb this into the main drain piping with T joing off to the side.

Or perforated pipe, again aiming north above surface, but with 2 90 degree bends so that the plumbing can go out the side wall of the tank and down into the main drain pipe from there.

Will the water draw be from syphoning or pump suction?

thanks

3 month ETA