Well, for starters lets just hit the brake on things.
Keep the filter media going so there is as much bacteria in this system as humanly possible.
Switching out the fake decor for live rock really isn't going to be a drastic difference at this point. Actual porous rock will give more area for bacteria to grow, but unless there are ammonia or nitrite readings in the system then everything has equaled out. You can add more rock to your tank pretty much at anytime.
The more pressing concern would be all the fish in the system, the coral beauty being one that needs a much larger tank to survive in. In the long term there will be issues even though they have not happened yet. Since you only have a local Petco like myself, returns aren't an option. Your best bet would be to upgrade the tank down the line. This would then open up for upgrades inside the tank, like getting yourself some macro/base rock so that it can become established and 'live'.