Why does the Torah write "Nega Tzara'as ki Sih'yeh be'Adam" and not the more common "Adam ki Yih'yeh be'Or Besaro Nega"?
Sifra: To teach us that the Din of Michyah applies even to a Metzora who initially appears covered with Tzara'as from head to toe. 1
See Torah Temimah, note 46.
Seeing as everyone distances themselves from the Metzora, who will bring him to the Kohen?
Seforno; Refer to 13:2:4:1.
Rosh and Da'as Zekenim (in14:2): We read "ve'Huva" like 've'Hu Va' (he comes by himself). 1
Oznayim la'Torah: The Torah is telling us that, even if the Metzora thinks that he is better off by leaving it as it is - seeing as until the Kohen declares him Tamei, he is Tahor, he is obligated to go to the Kohen.
Why will everyone distance themselves from him before the Kohen is Metamei him? We delay inspecting Tzara'as for a Chasan or during Yom-Tov, and people do not distance themselves from him? (PF)
What is the significance that the Pasuk begins and ends with the letter 'Nun'?
Rosh: Also 'Na'aman' begins and ends with a 'Nun', and two other relevant Pesukim. Na'aman asked a Navi ("Navi be'Kirb'cha? eilav Tishma'un" - Shoftim Devarim, 18:15) what to do about Tzara'as ("Nega Tzara'as? ha'Kohen"). Elisha told him to Tovel in the Yarden, due to (Bamidbar 32:32) "Nachnu Na'avor Chalutzim? la'Yarden." Which also begins and ends with a 'Nun'.
Moshav Zekenim: A tale-bearer or one who speaks Lashon ha'Ra (gets Tzara'as); it is as if they transgress the entire Torah, which was given fifty ('Nun') days after leaving Egypt). Haman, who was a tale-bearer on K'lal Yisrael, got Tzara'as, and was hung on a gallows fifty Amos tall. There are eleven such Pesukim - all of which do not contain a 'Samech', because if someone knows how to say them properly, no damaging angels will have power over him LeSatan lo - to prosecute against him. 1
Nachal Kedumim (Matos 13): Perhaps there are 'Nunim' before and after "va'Yhi bi'Neso'a ha'Aron?", to separate punishments.