NW wrote:

I was going to install a pond of approx. 6' by 10' with a section that was
around 3' deep. I'm considering scaling that back to be just a so called
"bird pond" that is around 3' by 4' feet and only 6" deep. I want the
sights and sounds of moving water but not a lot of maintenance. I'm going
to incorporate this into some new landscaping/hardscaping around the deck.

My feedback request:
- Can a keep a couple of fish in this size pond over the warm months? I
know it would be too shallow to winter them here in the northeast.

Yes. Goldfish would do fine in that - but make sure there's plenty of shade
(lotus would be nice).
- Is this too small for a good ecosystem to "run" on its own and will
actually require more attention than a larger pond?

It might require more attention, because you can't afford to let the water
level fluctuate much, but it's workable, and it needn't be much more work.

- Given that this would be my first pond, how likely is it that I'll want
something larger once I get a taste of having a pond?

Given that it's your first pond, it's about 100% likely you'll want another
one, soon. It doesn't really matter what size your first is - you always
want something else. I went from a bathtub, to a 200 sq.ft. 5' deep pond,
then to a bog (wet, but not submersed), etc...

- If I keep the surface area dimensions around 3' by 4' but go with more
depth, could I keep a couple of fish in there over the winter?

Most likely. I know of people who've kept goldfish in 18" in Toronto.
Depending whereabouts in the northeast, you shouldn't have a problem.
--
derek