1)
What is the meaning of "Al Aven Palet Lamo"?
1.
Rashi: To find salvation and wealth for evil. They hope to get reward from Sha'ul [for informing where I am].
2.
Radak: Do they expect to get salvation for the evil that they do to me?! No! [Hashem], lower them in Your anger, that they will not be saved.
3.
Malbim: The reason why "they hoped to kill me" (verse 7) is due to the 'sin' that I escaped. They thought that it was proper to kill me, and escaping was a sin.
2)
Who are "Amim"?
1.
Radak: They are his enemies from the Shevatim of Yisrael. (Each tribe is like an Am.)