Also, for your stock load, I'd build all three filters in series.
Vortex settlement chamber / triple filter / moving bed with 250l of k1 as stated above. You have an additional 2500 gallons of water filtration under heavy fish load with the Savio Spring Flow media in the triple filter as well as some bio with the Matala mechanical filter.
The triple drum setup is enough for a typical koi pond under heavy load for water volumes up to about 10,000 us gallons.
In ponding, for the DIY crowd, this is the staple filtration setup that had been used for many years only with a few slight variations.
Good luck.