The metal ring is fine. You can use the slots, that gives some adjustment later. Galv or stainless screws for the flange are fine. You align the bowl so it looks right to the eye.
Buy shims for installing your Champion. They tend to be a bit wavy on the bottom. That's why we install so many more TOTO bowls. You must be feeling lucky if you bought American Standard. I'm not a gambler. Good luck!
Here are Jamie's instructions for installing a toilet