Thanks BBL! This is my first time re-using yeast, so of course, I'm stressing out over minor details. I just figured making a starter makes more sense than pitching a cup of plain ol' yeast slurry.
Quick update - the 500ml starter is already producing 1 inch of foam after about 1 hour...so it looks like the starter is kicking into high gear. I'm going to pitch the entire 500ml, without doing a decant, tomorrow.