Hi and welcome to the forum! Your best bet would be to hit the beginners section and read up on fishless cycling. Try to take whatever your local fish shop says with a pinch of salt, remember they are out to make money! You are a good few weeks/months away from adding fish yet but it depends on what interests you, livebearers like guppies? schooling fish like tetras?
Sorry, just realised this was in coldwater area! Have you considered tropical? Your tank isnt really big enough for coldwater and tropical would be no harder to setup/run. You would just need to buy a heater.