Hi Andrea,
Sorry I misinterpreted your intent, here are my answers:
1. Lots of reasons: Initially for education, now for learning new development skills, design, making education a better place by providing plugins that enhance Moodle.
2. Around 20-60.
3. Community is diverse with individuals being specialised in certain areas. Seems to work well with a proper hierarchy of moderators to ensure things run smoothly.
4. Please could you give an example to explain the question with a list of 'types of relations' you are looking for.
5. No, it comes down to a much smaller group of users who work with developers to make things happen. I suspect a lot more bespoke tinkering goes on but its not shared perhaps as much as it could be.
6. Yes.
Gareth