Hi!
I've previously developed games in JavaScript and would be interested in working on your game.
I have a few years experience in Javascript. I can perfectly do what you want i.e. the sound effects and everything.
If you want me to add some features, I can only say about the no. of days required once I see the code and identify how the features have to be added.
If you want to deal outside Freelancer, we can do this for $350.
Let me know if you're ready to discuss further, awaiting your reply!