econ21, how exactly do you lower the battle difficulty? I play on auto-calc almost 100% of the time.. I'd love if I would be able to have a low battle diff and high campaign diff...

Btw, to the OP:

You should definately not stack up any garrisons larger than one unit (actually, I rarely have a garrison early on at all), and if you choose to garrison with a unit, make it a yari ashigaru.

Another thing: playing with Takeda/Tokugawa/Oda/Uesugi/Hojo is much, much harder than playing with other clans, diplomacy-wise. You simply can't make friends with everyone around you, and you are probably gonna face a two front war - at least I did in majority of my cases.

Two things I can add to that:

-Your neighbouring clans with low opinion of you (indifferent is low enough) are definately gonna be on the watch for you. If they have nothing else to conquer, they will be waiting for you to be busy somewhere else, or even better for you to lose a major army.
Imagine you have a full stack and ~4-5 provinces with good army production. You would survive losing that stack, but at that moment your Power rating would fall dramatically, and your neighbours would come streaming in.

-AI rarely waits for you to secure a front to involve. I played Uesugi, and I was destroying Date, but I still needed my armies in the north. Hojo then attacked me, I believe because they didn't want to let me have a protected back. It gave me many, many problems, cuz the provinces are huge and travel times long. That's something every TW game has - the AI doesn't want to let you finish an opponent fully before they come knocking (MTW has that for example).