1) I don't think she is an overrated singer. I believe she is one of the artists that has the voice of this generation. There are others as well
She has an incredible voice, but like Katie stated, those too young may underrate her voice. However, I really enjoyed the Back to Basics era. That really showed me her powerful vocals.
2) Genie in a Bottle, Beautiful, Fighter... etc. Yes.
3) I would go with Icon.
4) No
5) I think it is possible. She is great with ballads. Castle Walls gives me hope. I wish her the best.