Great questions. Technically you have to wait until payout to know exactly what you're going to get in rewards for a post. What you see throughout the week leading up to payout is only an estimate. It can fluctuate some. And I think it's best to make an introduceyourself post as soon as possible. It's not too late though if you've been on for a while and haven't yet. Go for it if you haven't yet and let them Steemit community get to know you.