If you plan on stocking further, maybe try another filter such as a Rena Filstar, for you the XP2 series would be a great addition to a 55. They are really easy to set up.
You should be ok with community tetras, they are hardy, but you could always add some things to the tank to soften the water. I would wait though, untill you have a basic idea of how to maintain your tank.
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I would be careful trying to soften the water, its probably better to maintain the natural pH/hardness of your water and get fish that normally hail from these water conditions in the wild.
For a 55 I would have suggested Lake Malawi Cichlids and your pH would be perfect for them. But there are plenty of fish that will do great in higher pH.