I *think* he's saying:
He wants to play a world diplomacy game with two teams (one team of 8 players, one of 9). The teams will be decided once the game has started (but before the first phase), by the team captain of the smaller team.
He is suggesting that he play as the team captain for the smaller team, and that the buy-in for the game be only 5-10
.
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If this is what he is suggesting, I think this is a bad idea. Surely the team that gets to pick their teammates will be at a huge advantage (and not enough to offset the additional player on the second team).
Perhaps a fairer start would be to have two team captains, and do a team draft after the countries are allocated? That said, I don't think I'd want to play that variant either.