You should take a look at the Facilitator Guide. It has more commentary on the various groups. I would say a minimum of six people (ideally 12 so that you have 2 for each group) - one for each role - to run it as a game. You might be able to collapse it a bit more, but it won't be as fun and you have to be careful to select groups to maintain tension.
If you have fewer than six (or maybe fewer than 12), I would recommend that you run it as an En-ROADS Climate Workshop (without the role play and you facilitating up front - perhaps also letting participants use the simulator before or after your presentation).
Do you wish to collaborate on this? There is every reason to get started on our climate emergency. Waiting buys us little and the need to begin acting is perhaps the main pillar of En-ROADS.
Good to know there are other En-ROADers out here!
I am happy to reply on here periodically, but I have taken on a new position and don't have a huge amount of bandwidth for a project like this. If there are specific, short term things you would like help with, please let me know.
When running the Game Format it is necessary to break into tables of stakeholder groups. The stakeholder groups have personas which guide how they act. In a video of a game simulation the groups were something like: