Wow - you really covered it all, Gia!!!!

I think I would go so far as to recommend NO gravel. Run the tank bare bottom. This will increase the water volume that will go in that tank, and allow you to keep it far cleaner. Less waste means less that must be processed int eh cycle, as well as less nitrate in the end.....
Youcan still add a few pretty stones or plants or whatever. The tank will look lovely and the fish will be happy.
A Penguin 150 is just exactly the right gph for the tank. But it has (unless they redesigned it and I missed it! - entirely possible) only the biowheel for the cycle platform. Biowheels seem to take a bit longer to colonate in a cycle, and, I feel, do not hold quite enough for a messy goldie. The 150 has no place for any extra biomedia to be stuffed in the thing. I have slit open the blue cartridges of the 150's I have and banged all the carbon out of the things. I then poured in biomedia into the blue cartridge so that there is still more area for the beneficial bacteria to colonate.
This makes it a bit difficult to clean the filters - I like to blast them clean under the faucet in the utility room and I cannot blast the biomedia, but active swishing and rubbing in used water does the trick. I have, on occasion, emptied the media into a bowl, blasted the blue floss and poured the media back in.
You can also or instead, drop a baggie of media behind some plants in your tank. This will work quite well, just not quite as well as having it in the filter....