When to start: this will depend on your access to venues, what your goal is like for attendance and securing speakers. A month minimum is a good guide*
Choosing a Date and Venue
Having a date and venue secured is the first major hurdle to organizing a successful event. It also is the first major validation of your efforts: it’s difficult to proceed with any other aspect of planning until these two key hurdles are overcome.
Also knowing the goal of your event or talk is key. For some it's obvious - e.g. the "School's Talk" is to educate children on the potential of remote work and to guide them on their next steps. But as your Chapter develops you will want to set a goal for your talks and events to help ensure success.
For the "School's Talk" make sure you speak to your contact to know what the venue will be like in the school. This may influence how you give the talk.
*But if you know you have all the required elements in place then go for it!