I mean technically, mine is one pump & one filter. Pump in the pond, filter above ground. I added the waterfall box but it's not required, I could have just had the water return directly back into the pond from the canister filter.
Main things to consider when doing mechanical filtration is how many times you need to turn over every gallon of water per hour you in your pond to keep it clean to your satisfaction. AND have a pump that can tolerate larger solids in order to not clog. If you get those two things under control...
I have 13 = 5 adults + 8 babies
I haven't cleaned it yet since installing
I do use a pool skimming net every afternoon to get floating chips & feathers but I only do it once a day.
The pump is able to handle solids and hasn't clogged on me yet
Here's what my water looks like right now
Cheapest is definitely going to be drain n refill....💯
And yes it's more than one item in the loop...here is what the loop looks likes like, minus the fish & plants
Here is what I have seen some have success with and what I am currently using. I'm using the waterfall box to add air exchange and put lava rock in the net bag of the waterfall box as additional filtration