A video run of the samurai scenario in Insane, maybe it might give you ideas, you can see the wave setup in advance, etc.
The Kunoichi shines as a very great distractor and even though the enemies always get the first turn (damn you archers) we are able to bear them using the well to prevent them surrounding us. Saving the items for emergencies or until the final wave.
The domination Card helped a lot to get back morale for Charm and Seduce.
Taunt is great to move enemies into a surrounded position.
The second siege is the hardest siege because of the unfair ambushes on wave 3 and 4.
Buy a pot and a helmet for emergencies, remember that your units can only carry two items, including the ones you bought.
You really need to be in the best conditions going in, as you can see, using a pot in the first turn is very advisable to avoid those archers. Taunt here helped a lot against them.
Third and Final Siege
You better spend all your money before the 3rd and final siege, I didnt, that was a mistake but not a fatal one. This siege was easier since the enemies have a harder time getting to you in turn one.
I also thought that there was 5 waves and saved the oil pots for it, but there are only four waves.
Watch out for those Katana Ronin, they hurt and their suicide attack is dangerous, try and finish them off with harpoons.