Endless questions..

No pix yet. Digi camera died recently. Soon though.
Just put in first plants. Hyacinth (makes me think of Jim Morrison)
and something called Thalia geniculata. Thalia tall & elegant. My
wife wants watercress but I cant find it here in San Francisco. Maybe
at the health food store.
Q's:

What is reasonable evaporation, or do I have a leak? Pond is about
400 gallons, 2.5' deep, and lost about an inch of water this week.

Can I build a plant stand out of copper plumbing pipe, or will the
metal cause weird brain waves (or other ailments) in the fish?

If I put sluggo, or diatomaceous earth, in the garden, and it rains,
and the runoff makes it's way into the pond, will it kill the fish?

Where's the best source of plants on the web? Is autumn an ok time to
introduce them (Zone 8-9 here, very rare freeze over winter)?

Thanks again.