I'd do just the single GT, and a bunch of cool dithers. IMHO, and 75 isn't that large, and I prefer to just keep 1 medium/large size cichlid in a 75.
Or just a single breeding pair of something SMALLER than a Midas. (Ex. Lyonsi)
I agree. I think long term a GT will do much better in a 75 than a midas. See if you can't get a male GT and then maybe a few male convicts or HRP's may work with it too. That way there's no breeding. I have giant zebra danio in with my central/south americans and they do well. Would look good! Good luck!