I'm about to expand my 400 gallon pond to a 1250 gallon. Yea!
Some background: San Francisco location, it never freezes. Leafy,
shady area. Pond is a large "C" shape (I know it's not ideal, but the
pond goes around trees & roots). The "C" is about 1' at it's
narrowest and 3' at it's widest. I've got 3 fish I think are koi (6"
long, with whiskers) and 5 other small goldfish, 2 perpetual tadpoles
and one frog. Also, I've currently got an Oase Aquamax 1000 pumping
into an Oase Filtoclear 800. with no skimmer and no bottom drain.
I'd like to have a skimmer & bottom drain in the new pond.

There is now a small waterfall I'm thinking of transforming into a
water-garden/exposed veggie filter (i.e., 3 levels of shallow pools,
each pool ~2' diameter, each filled with plants). Any opinions on
whether this should work well for water cleansing?

Biggest question: Any tips, suggestions, opinions about joining a new
liner to the old one? Anyone have success doing this, or should I
just spend the $ on a new huge liner? (Don't forget, the "C" shape
makes for a lot of unavoidable bunching-up of liner, whereas is I join
the old to the new, I can avoid alot of the bunching).

Should I keep the old pump/filter set and get another 'small' filter/
pump set (and use both at once), or scrap the old and get one larger
new set?