If you've just put your shrimp in, and are getting those 0 readings for ammonia & nitrite, it could well be that your shrimp hasn't really started rotting yet. Give it a couple of weeks to make sure. The nitrates could well come from your tap water; around here we have at least 40ppm nitrates.
As for your pH, it's true that things like cories come originally from soft water, so that would be an issue if you were keeping wild-caught cories. But the ones bred on farms, as all the ones you'll see in shops are, are much more adaptable. As long as you acclimatize them to your water gradually, they are fine. Our tapwater here comes from wells deep in the limestone, so it's a consistent pH of 7.8 and very hard. But I'm successfully keeping, amongst other things, neon tetras and kuhlie loaches which are supposed to like soft water. The only thing I would never try to keep in this water are discus. Also if I wanted to try to breed softwater fish (like neons) I might think about trying to find a source of soft water but for just keeping them, it's OK.
By far the most important thing for fishies is stability, so as long as your pH doesn't change, they'll adjust to it and be happy. The bad thing about trying to change your pH is that some of the ways you can go about changing it work only temporarily, and then the constantly changing pH is much worse for the fish than a high but steady pH.
But if you did want to match your fish's original environment to the water you have, mousey has given a really good list. I'll put in a vote for apple snails. If you are careful to choose tankmates that won't harrass them by nipping at their antennae, they will reward you by looking cool and exhibiting a range of interesting behaviors.
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