So the next step is for your wife to tell you that you're actually on holiday on the date you've chosen.
Speak the Skillsmatter and set another date.
Decide that if you are going to do it it'll be free.
Start mentioning the workshops idea to people and ask around to see who is interested in running one. Utilise what you have available, Twitter, Linkedin, Meetup, your contacts, etc.
Start mentioning that sponsorship would be nice.
Expect a whole lot of none responses as you're asking for money and no (direct) money will be made from this and people will have to give up their own time.
Receive a whole lot of responses and realise that your original idea of 3 rooms running parallel is now blown out the window as you've heard a lot of really interesting workshop ideas and you:
a. Want to attend them all
b. Are quite sure a lot of other people will want to attend them.
Start 'advertising' the workshops.
Speak to Skillsmatter and hear the good news that there are more rooms available so you now have 5 rooms.
Start chasing up workshop descriptions - Start this as early as possible, it'll take longer than you think.