I would not worry about the puffer eatting you live or dead rock, they will eat almost anything but I think they draw the line with that. As for when you should add the fish, after the tank has cycled let it sit with nothing in it for a couple two or three weeks, to make sure everything stays settled, test your water, and if everything is normal, I would add the puffer first, wait about a month then add the next fish. Remember the key to enjoying this hobby is patience. Good Luck