In my Otomo campaign, I've taken all regions on the island of Kyushu and a few regions on the nearest part of the mainland. I have 11 provinces (my largest AI rival has more than double that, this looks like an exciting challenge).

I've read that I should stop expanding and get ready for Realm Divide at this stage of the campaign, is that right?

I'm making trade treaties, researching civil techs, replacing unnecessary military buildings with markets (and upgrading them), upgrading farms and only upgrading castles which I expect to defend. I'm fighting a couple of small wars, partly to maintain my alliance with the Chosokabe and partly to give my troops experience - I'm not planning to expand (except very slowly). My allies control the island they started on. They also have trade ships on the trade circles at the western end of Japan, unfortunately - I missed an opportunity there. Are there other things I could/should be doing to prepare for Realm Divide as the Otomo?