Water change questions.

the tank that you are using for water changes does not need to be cycled.
it's not a bad idea to take water..de-chlorinate it and get it to the right temp prior to chnages..but it may not be necessary.
if you are taking RO water and then adding buffers etc..this is an excellent idea..but if you are just using tap water..you don't reallly have to do this step(tho this does not make it a bad idea)

Really no need for prefiltering your water so long as the source is nice and clean. Most municipal water supplies are perfectly safe for aquariums straight from the tap. All they require is a water conditioner to eliminate chlorine or chloramine.

Also no need to aerate as usually the pressurization necessary to get it up and out of your tap puts in so much dissolved gas that it will eventually "outgas" in a few hours; releasing thousands of tiny little bubbles over the course of the day.

That's a somewhat high pH so I am assuming the tap water has plenty of hardness...so you won't be needing buffers.

It's okay for a community tank I suppose. Personally I would work to soften it lightly. You can do that with a little driftwood. Don't go crazy with the idea of it though, as playing with water chemistry requires a lot of time, knowledge and patience and if you're just trying to keep a relatively happy community tank, there's not much reason to go into specialist techniques like peat filtration unless you decide a few months down the road to try your hand at biotoping.

For now your water is perfectly fine. And if you're considering livebearers it's actually quite perfect.

Certain rocks will indeed raise hardness and pH. That is why we usually look for types that are inert such as lava rock, slate, quartz, et al. Rocks like limestone and marble for example, contain calcium and will therefore contribute to increased hardness over time.

Rocks

Any limestone or corals will slowly add hardness to your water. Lots of African Cichlid guys use Texas Holey Rock or crushed coral in their tanks for water hardness. I use driftwood / plants / and almond leafs in my tanks because I want the tanic/humic acids making the PH lower for my pikes, plecos, and other SA cichlids.