I did not get to the divide yet, so I'd like to know how many provinces you can take before it triggers?

I expect that I'd want to capture almost that amount and then begin optimizing for the divide and anticipating attacks.

For me, the hard mode was ok for the battles, but for the campaign it felt a bit too limited as the economy only really allowed ashigaru units to keep the upkeep high enough.

I guess one part of the game is to try and pick out good provinces to conquer before the divide so they still will produce enough income and also have defensible bottlenecks in the map to allow defending with small number of stacks.

I also guess that it is a good idea to save up koku for the divide, so that you can run with a small income and still do some critical repairs/builds/recruits.