Adding money to a game of Risk
Be careful. Usually tinkering with houserules, if you overlook something, you can make it up on the spot. If there is real money at stake, suddenly the game becomes much more serious and the ability to quickly tweak something which might be in one player's favor or another is gone.

From your initial idea, I see several dramatic flaws. First is that Risk is designed as a winner-take-all game. You propose to have the ability to end the game short by unanimous-save-one consent. This will not work. One player, for instance, might have relatively few territories, but be well-fortified, well-positioned and have cards prepared for a powerful game-winning strike. Will this player be considered to be in the lead? If not, he will never agree to end the game. If so, he will lose out, controlling many fewer territories although the favorite to win.

You would need to make careful rules about when the game is allowed to come to an end. Can it be ended before a powerful attack? After an unlucky turn? Before whose attack--because the last attacker can just spread himself thin, without any regard to defense, and collect an unfairly large share of the pot.

With directed attacks, you may face accusations of favoritism or collusion that are much more venomous than in a non-stakes game. In this case, I think that playing Risk for money is a questionable idea, and playing with house rules to allow any stakes other than winner-take-all would be potentially disastrous.