Ask HN: How do you build and sustain an offline tech discussion community?

I’m considering starting an offline tech discussion group where people can freely share ideas and inspirations, without rigid formats like formal talks.

I’d love to hear advice from those who have organized similar meetups or communities:

What are good practices for keeping the atmosphere open but still productive?

How do you handle costs (venue, refreshments, etc.) and maintain a balance between expenses and income?

Any suggestions on long-term sustainability and keeping members engaged?

Thank you in advance for sharing your experiences!