[Opinions] Re: Roni and Ronnie (and some general stuff about nicknames)
I don't really like Ronnie on a boy (hate it on a girl), since I associate it with the douchebag idiot from Jersey Shore. It's kind of dated, and it doesn't really pop enough soundwise for me to like it despite the bad association. I think it's common enough. I've met one or two before.
As for a female Roni, I have never met a Ronia nn Roni, but I have met two women with just the name Roni. I would automatically assume it's a Jewish girl because the name is quite common in Israel and very rarely used outside the Jewish community. It's cute in theory, but I always draw the association to Rice-a-Roni. It's absolutely pronounced differently than Ronnie. Ronnie has a short O and Roni has a long one.
Ari is the best nickname you've got there for Aaron, but it doesn't really need one, I don't think. Ron is okay, but Ronnie from Aaron is unattractive and feels contrived. I'd say maybe Ronnie for Orlando...?