Actually, 7 goldfish wouldn't be very comfortable in a 70 gallon. They get too big. You could pull it off with overkill filtration and fancy goldfish (they're smaller and less active than sarasas, comets, and commons) but you still wouldn't be able to put in any decorations or they'd be cramped. It would be more trouble to maintain than you'd want.
And plants with goldfish? It can be done, but not in a heavily stocked tank like you're talking about. A few goldfish can be trained to leave plants alone, or plants can be situated in safe areas. But a huge crowd of goldfish will bump into plants even if they don't want to play with them.
I think you should go tropical because there is a better selection of midsize fish and plants, and you can fit many more into a tank. Angelfish are easy and get decent sized without being messy. Gouramis as well.
If you really want goldfish, get about 4 fancy types for a tank that size. You'll still be able to decorate it some and the fish will be happy and it won't be impossible to maintain. And they will be even happier if you DO heat it. Goldfish don't really thrive in cold cold water--at least keep them the temperature of your home, if not as high as the low 70s.