Anyone conducted a successfull Republican campaign, turning their backs on the anachronisms of Shogun and Emperor?

I've been trying it as the Saga but feel i need to save-scum and get my navy a bit better prepared for when I become everyone's biggest enemy. I think the realm divide threshold is lower in FotS than vanilla S2 so my relative strength is lower and the challenge hence greater.

Any pointers?

Also, if anyone has done it, how long does one need to conquer the requisite number of provinces? I thinking about how long I can turtle for befoer needing to make the big push. Kyushu is a good base for a republican campaign (i think) as holding the whole island and its outlying 3 single province islands leaves you 1 province short of triggering the realm divide.