I would find out what the GH is first and then choose fish that are suited to that. Unfortunately guppies and platies come from hard water and neons come from soft water. Putting them in water that is not suitable can reduce their life expectancy.
The pH and GH can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).