As for mentioning weaknesses, I think this can be a good move, but wisely. If you have specific weaknesses that you have already started to overcome, it can show your self-criticism and willingness to improve yourself. However, you should not emphasize on them. Instead, it's better to focus on your strengths and how they will help in your graduate school experience. Well, if you need professional help with writing, you can use here here personal statement writing help. They are awesome at helping with writing applications, I've used them myself. They do everything quickly and well, and the prices are reasonable.