I agree with the rest, don't add your fish to the new tank until it is fully cycled.
Can you fith the 55 under your tank, for a sump?
CC, I have never has a rock fish, but I bet he wouldn't like a CC substrate. They tend to bury themselves in the sand and CC can possibly injure them and will also limit any other sand stirring/sifting critters you might want.
Remember, the CC will stay on the top of the sand. If you mix the two, it is hard to clean the CC without sucking up a bunch of your sand. Trust me, I did that same combo and ended up just removing the CC. There are folks that love the look of CC and are perfectly happy with it, I wasn't.