The "Engage-at-will" command only pertains to projectile fire, either bow or musket. A 50/50 win/loss ratio is about right. As you read, the tutorial has about as much chance for luck as skill.

As for a general forsaking his honor...

If you want to learn the capabilities of units and game mechanics, I'd skip the tutorials and just set up some custom battles. Shogun is basically a "rock/paper/scissors" game. Spears beat cavalry, swords beat spears, and eventually the musket will rule the battlefield.

Once you get the hang of the game controls, I'd just jump right into a campaign...it's really the best way to learn Uesugi, Hojo, or Shimazu are typically good clans to start with. Takeda and Imagawa are a bit harder to manage, Oda is the most difficult for any starting date.