He was indeed a merchant, and later worked as Khadija's accountant (before he married her) when he received the revelation.

But he was a shepherd during his youth and was illiterate (even when he received the revelation and was a merchant/accountant, this is a period where a lot is based on oral communication).

Not sure about that "became a warrior" part (although he was what you could call a political leader, which included -in that time- participating in wars)