I'm pretty leery of just outright killing a daimyo even if they are minor ones. We haven't heard anything about Iwa taking them out through all of their engagements in the east, so taking them out might be an extreme escalation.
I'd rather court the local military and retrieve some useful intel. Plus if kill the daimyo, the ninja might call for assistance from a distant major power. Best not to create a vacuum we can't exploit in time.
1st option shows Ames hand.
2nd creates a power vacuum.
3rd might lead to diplomatic annex.
[x] Make contact with the paltry ninja force in the Land of Birds, they're the ones who are supposed to be replacing the regime after all. Though this will take the most amount of time, perhaps it will lead to the most stability.