1)
What was his suggestion "ve'Echoz Lecha Echad meha'Ne'arim"?
1.
Radak: Take him [captive] back with you.
2)
Why did he say "v'Kach Lecha Es Chalitzaso"?
1.
Radak: If you fear him, take his weapon - but do not kill him.
2.
Malbim: It is shameful for a Gibor to return empty in war. Take his weapon, and it will seem that this is what you pursued.