White Picket Witches: Preparing a Convention Game

On Saturday, there will be the first ever Gratisrollenspieltag (the German version of the Free RPG Day). I've volunteered to run a game of White Picket Witches with FATE Core at the FLGS in Nuremberg. Now, all I need to do is prepare for a four hour gaming slot. Time will most likely be to short to explain FATE, build the setting and have an enjoyable adventure. Therefore I am thinking about preping something beforehand and let the players fill in the blanks. My ideas so far:

• Give the whole session a theme/premisse to work from.
• Strip the game down to three families and prepare the name, a starting aspect and assign the type of magic practiced by the family. At the convention, I'll let each player come up with one additional aspect, until each family has three of them.
• Have a list of possible places of power prepared and let the players pick about three and design them.
• The character sheets will be half prepared. I will assign a name, a type of magic and some of the aspects (childhood to tie them together, heritage to tie them to the family; leaving canon aspect, tragic flaw and casting to be decided by the player. Maybe I'll do part of the canon aspect.) Also, the magic spell and a stunt will have been chosen already.
• Let them create two antagonists.
• Create one metaplot beforehand that will be the focus of the session.

That should cover me? Maybe as a back-up I'll have Mr Scratch and/or May ready.

The premise will be: "You are scions of the five families (well at least of three of them). You spend your childhood on the island getting into all sorts of trouble, and then left for college. Four years later, you are back together on Moon Island. You all have changed, but the island hasn't."

The three families will be named as Gardner, Gifford and Grant. The others (not appearing) will be Hargrove, Haynes and Howard. But the Howards have vanished.

• The Gardners are practicing Muscle Work and are "As one with the earth and the island".
• The Giffords are practicing Bone Work and are "As a blight upon joy and happiness"
• The Grants are practicing Breath Work and are a "Pillar of the community and the church"

Possible Places of Power:

• Abandoned Howard Estate
• Black Rock Forest
• Boat House Diner
• Canary Beach
• Moon Island High School
• Morgan Creek Resort
• Some other place the players think about

The metaplot will be "The families' crypts have been opened and the rest of the dead has been disturbed."

Do you think this will get me through a four hour convention game?