ובאת אל הכהנים הלוים ואל השפט אשר יהיה בימים ההם - Twice in the Parsha Rashi's says אין לך אלא שופט שבימיך (by זקן ממרא and עדים זוממין). Darash Dovid asks why it's repeated.
Yalkut Shimoni on the 3 prohibitions for a king and why the Torah doesn't give us the reason.
Minchat Chinuch: If we don't follow the Torah we are disobeying the words of a Navi (Moshe Rabbeinu), not listening to a Navi is a capital offense. Shouldn't every mitzvah be a capital offense?
The Kohen sends home 3 groups of people (newlyweds, etc.) which could be thousands of people, seemingly putting the army at risk, so as not to embarass those who went home because they were afraid of their sins.