Mlott, Neomaris annulata, a calcium based macro algae.
Temet, don't panic, you don't even have the rock yet LOL. Can't give you odds, sorry. Too dependent on too many things. I can tell you that buying fully cured rock with 2 day shipping will give you a lot of die off, which means ammonia, so I hope you're cycling with it! I'm OCD, that means you'll be able to remember & figure stuff out. Most hitchers are harmless, and if they're not they usually (not always) have to be in large numbers to cause issues. It's always good to have contact with others in your area, so join that club if there is one. Cultivate those friendships. Having someone come over & watch your tank is a bit much, though. Good descriptions & even bad pics have resulted in ID here, so you can always try. Just stop panicking! It will be fine & anything can be dealt with!
Cymonous, I can't get to the vid, sorry.