For heating you can buy a few standard heaters off eBay and use an air pump to keep the water moving so it doesn't freeze. We use a heater for our boat, but it was pretty expensive. Since its Florida the ground won't freeze so I'd imagine that putting it in the ground would not only look better, but it would provide some insulation. Floating pond plants like duckweed grow easily and can provide shade for your fish and "protection" in the fishes mind. You don't need plants or substrate if you don't want them, but I think it looks better. You could use small rocks as a substrate or leave it alone. Not sure about concreting it in, the ground should provide enough support if you dig the hole correctly. How much more is galvanized? I'd probably go with Rubbermaid just for cost effectiveness, but I think it would also look better. For a net I would use a bass or off shore fish net.
I just wanted to answer you so if anyone else has better suggestion feel free to correct me.
Good luck!