Due to the some what unpredictable nature of the AI one will also want to keep a close eye on long time enemies the Imagawa Clan, whom one shares an uneasy peace treaty with at the start of the campaign. So keep a close eye on relations with the Imagawa Clan to try and anticipate whether or not they are planning an invasion. As this can hamper plans to quickly deal with the Ogigayatsu Clan, due to the sometimes necessary redeployment of troops to your border with the Imagawa Clan.
On the bright side if the Imagawa Clan do invade and one successfully repulses them then often one can conquer all of the Imagawa Clan's provinces wiping them out of existence. From there one can either force vassal status on to the Tokugawa Clan through diplomacy, or take advantage of the Oda-Tokugawa war to nab at least a further one or two provinces.