Risk meets Dots & Boxes

First up, starting from the winning condition and working backwards is a good way to design a game.

Dots and Boxes works because it is simple, quick, and 2-player. Even then it has limited replayability because it is solvable.

From the sounds of it, you want a moderate complexity, longer, multi-player game. So there are a few issues to consider to make it fun.

I like the idea of the "last move wins" mechanic, however you would likely want to find a way to build this in throughout the game, rather than just once at the end. Otherwise you would end up with an hour of rather boring and ultimately pointless maneuvering followed by a single "Haha! I win!" moment. That game would be fun for at most 1 person, and possibly less than that.

For example, you could have special locations (cities, ley lines, shrines, whatever) which the races are all trying to claim, but only the player who claimed it on their turn gets the points for it. This way there are multiple "Haha! I win!" moments throughout the game. You'd probably want to make sure that the locations cannot be "unclaimed", in order to ensure that the game moves towards a conclusion rather than stalemating.

Another issue to consider is selecting which faction to control each turn. If everyone chooses Ogres every turn (because, for example, Ogres have the largest army and thus the greatest potential for expansion) then that would end up pretty boring once all the other races get wiped out. You'd need to consider this as part of your design.

For example, say there is a deck of cards/tokens with 3 from each faction. Players draw 1 token for their current turn to determine which faction they must control, and 1 for their next turn. Your "next turn" token is hidden from the other players. So on your current turn you could try to set things up to benefit the faction you're going to be using next, but that might also benefit somebody else who has the same token.

For example, a different way of addressing the same design problem might be through the use of special ability cards. So each player has a hand of cards which give bonuses if you use a particular faction (Merfolk get +2 actions, Ogres get +2 armies, etc), so the player can try to use the cards to maximise their own advantage.

Overall, I think the concept is rather interesting, in that the game is telling two different stories: the story of the factions battling for territory, and the story of the players trying to claim points. So in one game the Ogres might dominate, while in the next game the Merfolk take over the world, but you can still win regardless. Risk, in comparison, tells only 1 story because the player's progress towards winning the game is linked to the fate of one of the factions on the map.

I wish you all the best with your design.

Regards,
kos