are you sure it didn't just molt and is hiding out??
For rock, since you already have live rock, you can add some nice base rock. google marco rock. This is nice dry dead rock that will turn live over time and is a lot cheaper then live rock and since its dry, you get more rock them if it were soaked up with water.
good start on your tank.
For fish, you could add something like a bi-color or tail spot blenny. They like little holes in your rock and have a lot of personality