Hi EYG,

I'm sure it won't be long until someone posts a consicive guide for you.
Until then,
Try to play Uesugi. They have their back to the ocean and sit on very rich Provinces. If you manage to outtake Hojo very early, you can get hold of some of the richest provinces in Japan. Mori on the contrary sits on very poor lands and is more difficult to play.
The most furtile provinces are were Imagawa, Hojo and Uesugi meet.
So, a good starting position is important.
When building up your provinces, concentrate on income first. Build farming upgrades in the rich (300+) Provinces and build ports. Ports will get you a fixed amount of Koku every year. It's independent from harvest and you need no ships like in MTW.
Specialize your Provinces. One builds yari, the other Archers. Don't build all buildings in all Provinces.
Don't hesitate to disband ashis you once build to maintain loyalty. The upkeep costs for garrisons can add to a high amount.
Be careful not to build more troops than you can afford. Control this frequently. Use Shinobi and border forts to keep Provinces calm where taxes are high. They don't cost any upkeep and are very efficient.

When attacking, attack several adjacent provinces at a time to make the enemy split his defense forces. Call of the fake attacks and capture that single Province you want.

That's it for starters.

R'as

P.S.: Before I forget, the harvest messages are randomized. Nothing you can do to influence harvest.