In my previous home, I had a small pond of about 1,000 gallons. In
that pond I had started with a pump in the pond feeding a filter
outside the pond. Water returned through a veggie filter via gravity.
I'd say it worked OK but cleaning the pump of debris was a PITA so I
swapped it for a tetra retrofit bottom drain and an external pump. I
liked this much better.

In the new pond, about 5,000 gallons, I have an external self-priming
pump drawing water from a skimmer and two bottom drains and pushing it
through a bead filter before returning the water to a veggie filter
and two jacuzzi style jets.

I like the currnet set up very much. I like having an external pump
for maintenance, replacement, seeing whats going on etc. I like being
able to simply backflush the bead filter, I clean the filter and
change out the water in one fell swoop.

BUT, if I could do it over I would probably build the gravity style
filtration I see in the "Koi Kichi" book and other sources. There,
additional excavation is done adjacent to the pond and filled with
filter media. This additional chamber is fed by at least one bottom
drain and one skimmer. A pump then returns the water to the pond.
These seem like very clean installations, although it does mean more
work.

Good luck.