Interesting. I've never played the ronin faction using the original STW, only MI. In MI, they cannot produce strategic agents, so using shinobi to foster revolts in order to raise troops is not possible. They must have changed that in MI to make the ronin faction more challenging in the hidden campaign.

My usual strategy is to concentrate rather than attempt to maintain all three primary rebel areas. I raze and abandon Kaga, pulling all forces in that area towards central Japan (in my last campaign, Kaga and the surrounding territories remained rebellious for a long time despite not being garrisoned, yielding much-needed koku and generating additional troops when clans would invade with forces too small to hold the provinces without rebellion). I target the Oda for swift elimination and assume control of all of their provinces, making central Japan my base as a first priority (thus protecting crucial Yamshiro and Ise, and securing high-yield agricultural provinces, most of which also have port potential). Jimbo Naotaka, the four-star general in Etchu when you begin the campaign, is a significant tool in this process, and usually ends up holding the Eastern front in either Mino or Shinano for the early to mid parts of the campaign. I try and take Kawachi, Owari, and Mikawa as early as possible as they are river provinces and thus nice choke points that don't require a large and expensive army to protect effectively. They also have nice koku yields.

My second priority is to secure Shikoku and Tosa from invasion by the Shimazu and Mori (or Takeda, depending on who dominates their clash in the west). Once these two primary goals have been accomplished, I usually have a good bank going, and a nice infrastructure developed in Yamshiro, Tosa, Ise and Owari (just gotta love the Legendary Sword Dojo in Tosa that you control from the get-go --making defense of Tosa/Shikoku a high priority, particularly against the Shumazu ...). I then analyze the overall situation and decide what to concentrate on next--usually the biggest threats (particularly enemy infrastructure, which represent future enemy army potential). "Kamikaze raider" armies are very useful--armies formed specifically for penetrating deep into enemy territory to destroy key clan infrastructures, without necessarily intending to hold territory or make it back alive.

Lack of strategic agents in MI makes port attacks impossible for the ronin, so balancing expansion, agricultural development and trade for income to support the ever-increasing need for military might is crucial. I enjoy ronin faction campaigns when I'm in the mood for a purely military expansionist agenda.