Personally, I really liked the idea of Harry putting the chamber to good use, I always thought he underused a secret location only he could access.
Storywise, I thought that a few aspects were a bit rushed and could be fleshed out a bit more to give it more depth. For example, Harry instantly trusting Daphne w/his animagus brewing seemed a bit quick, I could see him showing her the chamber, but leaving that revelation for when they're closer friends. (other ex. meeting the magical snake, training to become more powerful magically rather than just stating it).
Overall, I found it to be a very intriguing and interesting beginning and I look forward to the next chapter. (Well Done!).
Ps. As for animagus forms, I always thought Harry would make an excellent bird of prey (eagle/hawk) w/his love of flying and propensity to fall off his broom ;). As for Daphne, not so sure as we dont know much about her.