“Every registered Republican can participate in the conventions.”
I think you meant to say that every registered Republican can vote in their local precinct caucus to select committeemen to represent their best interests at the county convention. I’m pretty sure that it is just those delegates that they elected from their precinct that can vote at the county.
Maybe. I had heard something described as district conventions that selected delegates to go to state conventions. Whatever the process, it does start at the level of voters voting for candidates. Trump, er, Drudge Report constantly claims these are “voterless” elections, which is just flat out false.