1)
Where do we find that Ohavei Hashem are like the sun?
1.
Rashi, from Targum Yonasan and Tanchuma Bereishis 6, based on Yeshayah 30:26: In the future, they will radiate 49 as much as the sun does in seven days, i.e. 343 times as much.
2.
Radak: Just like the sun rises and gets stronger, until it is at its peak strength at noon, so Ohavei Hashem get stronger.
3.
Malbim: Clouds do not darken the sun (totally block its light); the same applies to Tzadikim.
2)
Who said that the land was serene for 40 years?
1.
Rashi: It is the author of the Sefer (and not Devorah).