Hi Daniel,
Great that you want to start a chapter, it's great fun ;-)
Here are a few things you'll need to consider:
- find a venue: I like to pick one already equipped with computers, such as a school,a university, ...
- find co-animators and helpers: from my experience approximately 1 co-animator for 5 children
- select a date: saturdays work fine
- select your workshops: depending on what you have, your budget, there are plenty of choices, even with zero budget: scratch, codecombat, minecraft modding, ...
- craft a page announcing the event + registration mechanism (can be a simple email, or eventbrite, ...). I use jotform integrated with a google spreadsheet.
- promote the event
In all cases, start small (small number of workshops, small number of childen, ...), then grow from there over time.
Hope this helps to get started.
Cheers,
Stephane