Not sure what your overall objective is, but you may want to design with the intent that the water is removed from the surface as it condenses and not allow it to freeze on the surface.
I would agree with this, since I built something almost exactly like what you are doing. I had a peltier cooler hung with a heatsink on it so that it would drip over a funnel with a small hole into a reservoir. This was with a 60 watt cooler and due to the constant flow of water, it would not freeze.
It would collect about 1/4 cup in 2 hours in my 90deg 90% humidity garage.
This would simplify your project a bit. The addition of a small fan would also help prevent freezing on a more powerful unit, as would a larger heatsink.
Also, if you don't freeze it and use a fan to circulate the air, you can route the excess cold air from the cold surface to the hot side, making it more efficient.