Oh, I remember this same awkward, lonely search myself, Leah. It was the reason I started the ExCharisma group all those years ago before moving it to the-highway. I too am a "Calvinistic Baptist," formerly Presbyterian (here is why), and Charismatic (Pentecostal, kinda sorta) before that.

I'll take the Regulative Principle of Worship (RPW) question (it's also described in the "why" article in the above link): It means that God is the One who tells us how He is to be worshiped; that we are not to "invent" new ways of worshiping Him that He didn't command. In other words, the RPW forbids human inventions that we think will please Him. It forbids superstition, in other words, which I define this:

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Superstition (su-per-sti-shun), n., anything imagined, invented, or attempted with the intention to appease, curry favor with, or otherwise please the Almighty, which is not found holy Scripture.

He tells us how He is to be worshiped! We are not to do what we imagine might please Him because it makes us feel "spiritual" or gives us a thrill. Every tradition has it's extrabiblical inventions, from "making the sign of the cross" to "the altar call." I think it also applies in a broader sense, but that's a whole 'nother subject, "credo-vs-paedo," not going there again, lol.

I hope that's helpful.

-Robin