The map will probably give some issues here. If you put all the players in the same map you are bound to get problems. Players trying to kill others with lava, fire or even water. Or the ones who just stand in front of others to make them unable to break any blocks. And remember what happens when 2 players are in a 2x1 area? They can't get out. Maybe it would be best to put everyone in a separated area, but that might just take the multiplayer aspect away. And then there is the popularity, I honestly think most players play minigames for the PvP, it isn't a coincidence that multiple people already asked about possible PvP in this minigame, if you actually want people to play it it might be a good idea to get it in there somehow. And the question is or people will still find it fun to do after a few games. Maybe if you change the area they are in and the things they have to craft, but it remains limited if you ask me.
Despite everything mentioned above I still really like the idea, and I'd certainly play a few rounds^^