I've got a very similar setup and dealt with the same questions over the last year.
The question of how much filtration turnover and getting even flow are separate issues. Good advice to be conservative by assuming ~half the manufacturer's spec on gph.
Regarding flow, one consideration is the type of fish. Rainbows will appreciate a river-like flow, while others prefer a much gentler flow. I agree that adding powerhead(s) (perhaps small ones) will give you flexibility based on your scape and intake/output placement.
With a tall tank and also wanting glass, I struggled to find a long intake tubes and pipes that would get CO2 as low in the tank as I'd prefer. I found "Violet" pipes vs. more common Lily pipes angle the flow lower into the tank. I bought steel intakes with skimmers just for looks compared to my prior functional but not so pretty, green Eheim stuff.
One nit / tip for setup -- when connecting inline heater, inline reactors, the orientation under your tank might be tricky. Please wait before cutting excess length of your hoses. If your change your intake/output locations to adjust flow, you don't want to find yourself short of needed hoses. In my case an "X" setup with the left canister output going into the tank on the right and visa-versa made it easier to orient the inline gadgetry.
Walking the tightrope of discus in a high tech planted tank.
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