It's a good thing to start off with an expert meeting - this way the team will get to know each other and then you can start working on the project.
In an expert meeting your core team is coming together to work on the project. Here the basic group work is done that you will be presenting in the main workshop.
The central component is the workshop, where your team will be presenting the first outcomes and ideas to a broader public of experts. It should give you new ideas and in depth views, and it will allow you to meet interesting people who might get involved in the subject.
If your team has a lot of work to prepare a first, substantial outcome (maybe because it's a really new idea) it will be a good idea to have more than one expert meeting before the central workshop.
A network meeting is typically held after the central workshop to follow up on specific aspects of your project. Ideally, network participants will be recruited among participants of the previous workshop.
While all of the above take place in Graz, Austria, national events and regional workshops will be held in a member state of the ECML to work on a specific national or regional aspect. You need to see if this option is important for your project.
It all comes down to the main question: which activities will work best to develop your project successfully?