I wouldn't worry so much about the PH - a steady PH is better than a fluctuating PH. A lot of fish will adapt to what you can provide. When you start messing with increasing then lowering then maybe back up a bit, that's more stressful. Is there an issue with just using your tap water with a dechlorinator like Prime?
As previously mentioned, you should cycle the tank first - without fish. Less work (fewer wc's) and no unnecessary fish deaths. You can start with plants while you cycle. Try some crypts, maybe anubias tied to a piece of driftwood.