It’s customary to follow an introductory phrase with a comma unless it’s really short and doesn’t seem to need one. You’re never wrong to use one, so I would recommend taking the guesswork out of the whole ordeal by just using one there.
This one is pretty easy. A noun in direct address just means that you are using names or labels of some sort to get someone’s attention or to speak directly to them. When you put this in writing, you need a comma to separate the name or label from the rest of the sentence.
Consider this conversation.
“Sweetie, please go down into the basement and bring Mommy the box of spiders that we’ve been saving for Halloween.”
“No, Mommy! Please don’t make me!”
“Don’t worry, Smuggims. They’re not real.”
“But they still scare me, Mommy!”
“OK, Punkin-Poo. Mommy will do it this time.”
“Don’t be mad, Mommy. Maybe I could do it when I turn five!”
“Sugar-Face, I’m not mad. It’s just harder for me to sneak past the ogre who sleeps next to the furnace.”
“He’s not so bad, Mommy. He likes me! Me and Daddy always bring him tasty chum left over from our fishing trips.”
“Really? Then here, my little Huggy Bear, is what we’ll do. We’ll hold hands and go down into the basement together! You can distract the ogre while I get the spiders!”
“That, Mommy, is the best idea ever!!”
Our nouns in direct address, then, are Sweetie, Mommy, Smuggims, Punkin-Poo, Sugar-Face and Huggy Bear. Notice that they are separated from other elements in the sentences by commas no matter where they appear.
Write a ten-line conversation between two people. Call them Calista and Zeus. The situation they’re in is up to you. They are speaking directly to each other in each line. Be sure, for practice, that you place their names in assorted locations in the sentences and that you separate the names from the main parts with commas.
Have fun with it!!