@Jenova : Made that choice, met Eros, but I was on a Green save from memory ? Maybe the default choice include helping Medusa.

I may be wrong, but to be visited by Medusa, she needs to survive in the first game, for that the only way is to have a Blue save and made the choice to help her at the end of the song and not speak about her with Athena later on.
Otherwise, no matter what you'll do, Medusa won't be there anymore, at least that's what is implied, both in text and in the final scene as she's present only on Blue choice.

If you want to enjoy Pan route the best (choosing him instead of Freddie at the beginning of Stray Gods), blue will be the best choice as Grace will be as much as a Greek Mythology buff as Freddie and you won't feel like an idiot all the time.

It seems that to meet either medusa or eros you need to pick between a guy with a phone or a woman with strange hair at some point at the speed dating. Choice is only between two of them at the same time and he even compares hair with medusa's snakes.
Worked for me with the same save from the main game.

Okay, that's interesting. Thought that had more impact than it did. At the very least, I got unique dialogue for continuing off of a save that I chose to help Medusa in. It was weirdly comforting to hear how she's improving with Apollo's help.

to meet Medusa I managed to use the default save. after a few play throughs it seems to meet Medusa, you have to fail and have no hope during the speed dating. leaving early, pointing out the prospect's faults is what i believe determines if you meet medusa.

Good so far, but you're missing a few. Allow me to offer a hand.

1. "In Search of Fate"

Choose the "I want a quest" option (blue) as the final option in Grace's song (Something New). Orpheus will then go on a quest in search of the fates.

Side note, I think the outcome (and achievement) of the song depends only on the final choice, and not the preceding choices. I've only played around enough to get the achievements though, so I'm not sure about this.

2. "Orpheus Has No Rizz"

Flirt at all three opportunities given to you (and fail). This is Eros/Medusa depending on the choices leading up to the bar, Hermes, and Grace.

3. "Return of the King"

This requires you to continue from a playthrough of the base game where you chose to give Orpheus the throne. The lead-up to the first song will play out differently (and you get to see Cerberus!), and the achievement will be granted to you after the first song similarly to "One More Song".

I'd also like to note that I don't think destroying the throne is the "default" option for the DLC. I did my first playthrough of the DLC with the default options, and then later continued from a save where I gave the throne to Persephone, and the opening dialogue was the exact same.

Finally, I'm curious about "Outside Looking In". Did you not need to continue from a save where you offered Apollo's help to Medusa during her song in the base game? Were you just able to meet with her regardless? I thought that's what you needed to do, so I continued from my save where I did that.

Overall? Good start. Needs some more information and some spell-checking, though.