Ok,

No substrate then.. pity because you can see the bottom of the pond
quite well because it is so shallow. I presume in a couple of months
time the liner will have pretty much disappeared and have be replaced
by algae and brown mud?

Goldfish.. yes, I can't really work up much enthusiasm for them at the
moment. My (now) wife brought a tank and three goldfish home one day
(far too small tank, no decent filter, 2 causalities within the first
3 days). That was about 15 years ago, but was what started me on the
aquarium hobby..

Unfortunately, I'm not a big fan of the terribly overbred varieties
that can hardly swim properly and are prone to eye infections, etc,
etc.. so for me it can only really be the hardier, single tailed
varieties.

I haven't looked much into goldfish since we got our first tetras..
our house was planned with my 1000L discus nature aquarium project in
mind, but now that we have become parents that suddenly looks like a
bad idea; at least for a few years.. that's what got me a bit worked
up about the whole pond thing :-)

I just can't help thinking that going from Discus back to Goldfish is
step backwards.. I know they can be great fish too, but they are a bit
"garden variety" and remind me of the poor sickness-ridden fish in our
local chinese restaurant. Koi would have been a much more respectable
hobby.. It does not help that Wikipedia refers to Shubunkins as "poor
man's koi" :-)

Still I'm basically a pond newbie and should cut my teeth first.. so
it's single tailed goldfish: "common" or "comet"..

Shubunkin is a fancy term for "calico" I suppose? certainly sounds
better.

Wakin are double tailed and, if I remember correctly, will thus be
eaten for breakfast by the single tailed varieties. Right?

Sarassas: are these basically all white or white and red comets?

I can't remember whether you can mix "comet" breeds and "common"
goldfish safely?

So basically my only real choices would be to go with:

1) orange "comet" (plain old comet)
2) white "comet" (Sarassa)
3) white & orange "comet" (Sarassa)
4) red, white, grey and black speckled "comets" (Shubunkins)

... and that’s that.

Are there any other compatible cold water fish?

...and what about housing koi with goldfish.. I suspect that the
goldfish will soon have disappeared? So once I get my courage up and
have a go at Koi keeping I should get rid of the goldfish first?

Sorry about the persistent interrogation.. I really do appreciate all
the expert advice I'm getting here and will try to post pictures once
the first fish arrive..

Thanks again for your help.

Frank