Hello,
You'll want from 1 to 1.5 lbs of live rock per gallon and at the very least 10x per hour water turn over in the tank. Multiple power heads will work a lot better than one big power head as well. I would have some sort of filter or sump set up so that you can run carbon as needed due to meds, detritus etc. in your water. IMO it's best to keep your set up as simple as possible the less stuff you have that can go wrong the better off you are.
Even a baby Radiata Lionfish will quickly out grow the tank you would be much better off with a dwarf a fu man chu etc. They would be more than a few month inhabitant of your tank. I have no idea what a pineapple fish is and couldn't say if it would fit or not.
hth
Max
