You didn't consider cloud formations. If there are lots of clouds but the sun is at a peak, more get's reflected before it get's to Earth and leads to cooler weather than if the sky is clear. If the sun is at a low but the sky is clear, it can more easily reach Earth and lead to warmer weather, yet with cloudy skies can lead to much cooler weather. The warmer and cooler weather also effects how and when clouds form, so they directly effect each other.
Water is actually one of the biggest culprits to trapping heat.
Correct. This ties into cloud formation. Just another link in the chain.
CO2 currently only makes up around 0.04% of the entire atmosphere, while water vapor varies and can be from 0.01% up to 4.0% depending on temperature and air density.