Great idea, many are playing with. Have you considered making some research on what's already out there and how your sister website will differentiate? Maybe by integrating LN prizes?

Here some:

This reminds me how most of the bitcoin communities are organized. SatoshiSpritz has a similar approach, displaying all the communities in a map and for each community location there's a telegram group. This need a responsible person on each location to create and administrate a chat group. The setup is a bit rudimentary, but probably has been working as I see it reflected in other bitcoin communities too. If not using telegram, they use signal, matrix, or other similar group chat apps.

Considering building a custom system as you mentioned #1068818 with custom functionalities could nice, but it does not guarantee the communities in each location to know about it or even use it. I'd start simple and use tools that anyone is familiar with to begin with ad evaluate how things go.

And I agree with @perscrutador, you'd need to create value an incentive for people to connect and look at the website but also to the comms channels, whatever is the website itself or the messaging apps suggested above. Implementing elo, rankings, and points, whether between players or teams¹, will be a great incentive, and you can initially do it with an online spreadsheet.

This process could help you build a mvp, structure the data and the comms chanels, find reps in each location, and in general, simply validate your idea. Was not expecting to write so much... You can tell like the idea!