Ok, so first things first, don't panic.  I got the cure for what ails you.  Yes, between character creation and stories, your first session is largely booked.  As for an intro adventure, here is what I ran as a test adventure.  While it's open ended and could be used to jump start a campaign, I'm not sure I would recommend it.  I wrote it when only the core book was available and it leans much heavier on 1st edition lore.  But I think it holds up as a solid outline for how to write your first adventure.  Plus – here's a dirty little secret – you don't need an intro adventure.  Your players are going to write it for you.

Here's what I mean.

Before you start your session 0, you are going to need to decide a few things:

• What is the theme of the game?  Pirates, Musketeers, Explorers, Ambassadors, Wandering Heroes?  Before your session 0, pick three that appeal to you and poll your players.  Have them rank your three choices in the order of preference.  The one that scores the highest is going to be your game.  Now we have a place to start.  If you want, look over the themes in chapter 1 of the core book ("Welcome to 7th Sea") and poll your players on those too: what 3 themes most appeal to each of them.  They don't have to rank them, just pick three.  Piracy?  Intrigue?  Romance?  The ones that get the most votes you are going to incorporate into your game.  Having these choices on hand will also help you guide them through character creation and the writers' room.  Got that?  Cool!  Moving on.
• Where do you want to start?  Before your session 0, you'll need to decide on where you want your game to begin.  The players choices can help with this.  What nation appeals to you?  Each nation has a theme.  Eisen is monster hunting.  Avalon, faerie tales.  Castille, science vs faith (kinda).  Now dial it down further.  Pick a city or a town.  You don't need any particular reason for this: either you start something in a big city full of adventure, or proximate to a landmark or city.  Again, the themes your group chooses are going to inform a lot of this.  You can't really run a game of Diplomacy and Romance in the middle of Eisen wilderness.
• Who is the Villain?  Yes, you'll want a villain for this excercise.  You can pull one out of the Heroes & Villains book if you have it or just invent one whole cloth.  Your villain threatens the themes your players chose.  You need to choose how.  Pick two of these to be schemes.  Don't worry about Influence costs or any of that business at this point.  Just give your villain a Rank and two things to do.  For this outting, go with a Rank between 8 and 10.  Don't worry about Arcana or Advantages, except decide if the Villain is a duelist or a sorcerer (or both!).
• Finally, choose a focal point for your first scene.  In The Island, its a storm that leaves the heroes shipwrecked on an uncharted island.  It could also be a festival, a wedding, a parade, a hunt, a chase, or a masquarade ball.  Something grand and over the top.  This is how your session is going to begin and where you are going to put your detail.  Because your opening scene is the one place your players can't really object to or avoid.  When you do this, be sure to note some ideas of potential Risks with Consequences and at least one Opportunity.  Remember, most Risks apply to the whole group.  So you'll want at least 3 consequences that will apply to EVERYONE participating in the Risk.  Three is a good number for this.  A good first scene should end by presenting the heroes with a problem to solve.  It doesn't have to be a complicated one, or have a lot of moving parts.  If it sounds like fun, that's good enough.

​Session 0: Keep it Simple.  Keep Session 0 for character generation and story generation.  Because those stories are going to fill out the rest of our first session.  Now, a warning.  Your players may give you a bunch of blank expressions when you start prompting for stories.  If this is the case, no worries.  You just need them to give you something.  A mentor, a loved one, an object of affection, a rival. Use the list of 20 Questions as a guide.  Because we are going to use these to fill out our first adventure.

Ok, so now you have all the pieces of a cool first adventure ready to go.  You just need to assemble them, add a glass of wine, and some cool set pieces.

Take your two favorite ideas from your players stories.  We are going to use those – the first steps anyway.

So now our adventure looks something like this:

• An opening scheme that presents a FUN problem to be solved (this may or may not be related to anything else in the list – if it is, great!  If not, no worries).
• A villain with 2 schemes to achieve.  These schemes are things that threaten the themes the players chose earlier.
• The first steps of your two favorite hero stories.

Now just arrange these elements how you like them and you are ready to go.  As an outline, it's probably going to look like this:

• Opening scene
• Personal Story 1
• Villain Scheme 2
• Personal Story 2
• Villain Scheme 2
• Finale (Resolve Opening Scene Problem)

That's six scenes.  So assuming each scene takes about 30 minutes to resolve, you have 3 hours in the bag.  That leaves you room for at least 2 more scenes inspired by the heroes actions.  And you can always drop one of the villain schemes if things are going good.

Lets talk mechanics.  Don't worry about Dramatic Sequences.  Save those for a different session.  Don't worry about dice rolling – assume the heroes succeed in most of their endeavors.  This session, mechanically, we only want to include three things:

• A standard Risk: to teach the basics of the core mechanic.
• An Action Sequence vs Brutes: to teach the basics of an action sequence and to make the players feel AWESOME!
• An Action Sequence vs Brutes and a Villain: to reinforce the action sequence mechanics and turn up the heat a little on the players.  

Finally, let's go back to the villain.  Don't get too attached to him at this stage.  So aside from the Rank (remember, 8-10) and assigning a duelist style or a sorcery, you don't have to do anything.  If one of the players creates a Fate Witch character, THEN you will want to assign an Arcana.  If more than one player creates a duelist, raise the villain's rank by 2 for each duelist in the group (no more than Rank 12, though – you just want him tough enough to last a couple of rounds against the duelists).  

So there you go.  A recipe for your first game session.  Don't worry about screwing up.  If you keep the mechanics light, it won't matter.  Fun will be had.  And you'll have more juice going into session 2.

Does that help?  

ps. I highly recommend listening to an episode of Tabletop Radio Hour or Essential NPCs prior to play.  Both will give you an excellent idea of how the game flows.  Or, take a free trial of Project Alpha and watch the last season of Starter Kit.  Just be warned, John Wick doesn't stick to the rules of his game.