Opinions on filter design/pipework layout etc....

Planning my first pond & got to the point of working out how to hook up the
filters etc......

I was planning on having an external filter at the same level as the pond so
that water will flow into it & then putting some kind of pump on the clean
side - the logic being that it would be better to just suck the rubbish out
of the pond into the filter (possibly into some kind of catchment chamber
first) rather than "liquidizing" it through a pump before it gets to the
filter.

Assuming I do this then I need to get water out of the pond - a bottom drain
looks like a good idea but cutting the liner down there looks like an
"interesting" thing to attempt & also presumeably I'd have to dig a trench
of some sort under the line to accomodate the pipework....

Another solution I was advised to look at was to have a bottom drain that
just went to a waste pipe so that periodically I could just open it & suck
the rubbish from the bottom of the pond straight to waste. Then to mount the
outlet for the filter about halfway up the side of the pond. The other
question related to this is as to whether its worth putting in a surface
skimmer or not.

The area my pond will go in naturally restricts the size it can be (we are
only talking about 1000 gallons or so). However, there is a redundant (and
non visible) area close by where I was considering placing some larg-ish
water tanks (with lids on) - the idea being to pump water out from the
filter upto these which would then overflow back to the pond. The idea of is
to increase the overall water volume of the system.

Has anybody tried to do something similar & what's the general view as to
how succesful/beneficial this might be? I could potentially increase the
water volume by between 25 & 50% by doing this (at a rough estimate).

I've kept aquariums for a number of years so I know a fair bit about water
chemistry & management, filters, bio cycles etc but this will be my first
pond. I grew up with ponds in the garden but these were always completely
unfiltered & seemed to do OK (depending on the weather and the frequency
with which the Herons visited!). I would like to try & build something that
needs relatively little maintenance & although I might put a few Koi in it I
do want to have some plants etc to make it fairly natural looking.

All ideas gratefully received.

I.