In what regard is the Torah comparing the goat of the Chatas Yachid to the Zevach Shelamim?
The same answer applies to the Chatas Yachid of a lamb in Pasuk 35, only there it comes to add the Alyah Temimah (Rashi and Rashbam).
The Torah, in this Pasuk and in Pasuk 35, discusses all the Chelev. How about the kidneys and the Yoseres ha'Kaveid?
Ramban (earlier, on Vayikra 3:9): "All the Chelev" incorporates all the parts that are separated together with it.
Why is Re'ach Nicho'ach written about a commoner's Chatas, but no other Chatas?
Hadar Zekenim (3): Hashem is more exacting about great people when they sin than about small people. Refer also to 4:26:2:1 and the note there.