(Turabian citation) 
You summarised the significance of the cross in Paul’s thought nicely and your summary of the pivot in Paul’s life from church-persecutor to church-builder is very helpful. I think I’d emphasize more of the continuity between Paul’s pre-Christ work and post-Christ work. For example, I agree with many scholars who don’t find the language of “conversion” suitable to refer to Paul’s Damascus Road experience; I think it anachronistically assumes a kind of modern category of religion and distinction between Judaism and Christianity which probably doesn’t apply to that period in time. That’s not to say that the change wasn’t dramatic or profound for Paul, but he basically goes from supporting one version of ancient Judaism to another one and his new identity is as an apostle of a Jewish messiah, etc.