I would go with goldfish for this scaled back trial... No heater required and they are available at local pet stores as "feeder fish" for about the price I was able to find my tilapia for in bulk. I agree with the bare floor of the ft. The gravel in the frowned will act like bio media, but if going with a raft system I don't see why you couldn't place a media box in between the ft and gb... Much like a canister filter... Best of wishes and I cannot stress the "over usage" of activated carbon for keeping fish odor down to keep the wife happy!!! Best of luck!