1)
What sparked off Moshe's anger?
2)
Why did Moshe, Elazar and the Nesi'im all go out to meet the troops as they returned from the battle-field?
1.
Rashi: Because they saw the boys running out to grab some of the spoil. 1
2.
Rashbam: To prevent them from entering the camp, seeing as they were all Tamei Meis.
1
Presumably, this will also explain why the Torah inserts this Pasuk ? after the reference to the various types of spoil ? in spite of having already stated that they brought all the spoil to Moshe and Aharon.
3)
Why did the soldiers need to be purified?
1.
Rashi: Refer to 31:19:1.1:1.