I suspect this is more than sufficient filter flow
- the big slow downs on filter output are when inline heaters & CO2 reactors etc are installed
- in tank, loads of hardscape whether rock or massive (solid) wood will significantly impact flow
You may want to play with outlets to see what impact these have on flow in your tank - easiest is when tank is still just glass, water & filters as you can then just drop in a bit of "color" & watch the dispersal ... beet juice is quite good
(& cheap & rather simple to obtain & no worries on additives) or choose any of the aquarium meds that are nicely colored - tanks looks to have black silicon which is always nice as it doesn't show color stains or algae
Once you've a good idea of what your filters & outlets will do, then add in your hardscape & test it's affect on your preferred outlet pipes.
As you're running 2 filters, you can choose just one as the biofilter or add lesser volumes of media to both - I'd set up the filters as I intend to run them during the flow experiments.
Must ask, why all the double taps?