Sorry, but Venus Fly Traps just don't get too huge. Even under the best conditions, traps only get to be about 2 inches long and plants are only about 8 inches across.
The things that you write will get you there. The biggest factors are lots of sunlight and good, clean water. I have also read that placing stones around the plant that will trap heat and keep the plant warmer longer after the sun goes down helps the plant grow a little bigger. I haven't tried this technique myself.