Answer to Question 1
At spring tides, the Sun and Moon act in concert, making for large tidal variation. At neap tides, the Sun lies 90 degrees from the Moon at quarter phases, and largely cancels out the tidal pull of the Moon.
Answer to Question 2
Since even a small change in temperature, raised to the fourth power, would result in a large change in the total solar energy radiated, if the Sun had cooled much, our oceans would have frozen and life would have ceased to exist here.