1 - Pietro's greatest strength is his desire to be a good person. He tries really, really hard and just kind of... Sucks at it. His greatest weakness is probably how quickly he judges a given situation. It's not necessarily that his judgment or opinions are bad, it's just that he makes them so quickly, he doesn't have time to second guess himself.

2 - He'd say his greatest strength is his speed and his greatest weakness is his inability to play nice with others. It's not really his fault though. It's part of his mutation and thus a necessary evil.