The Chosokabe are ideal for going Christian. Because Shikoku is an island you will have relatively few worries about invasions while you suppress the unrest that follows on conversion. Nanban trade quarters increase your trading potential from 3 to 5, reducing what is in my opinion the biggest drawback to the Chosokabe starting position.
After conversion you can use Christian missionaries to spread rebellions, opening up opportunities to make landfall while avoiding costly wars. An added advantage is that battles against rebels rarely result in memorable victories, so they don't drive up your fame, allowing you to take an extra province before realm divide. On legendary difficulty, I took all of Shikoku + Kyushu + 3 provinces at the southers end of the mainland + Sado, and I built five legendary buildings, all without triggering RD.
(I use Sado as a base for raids during realm divide. While I take all the provinces in the south for myself after RD, I launch an army from Sado to take vulnerable provinces at the other end of the map and turn them into vassals so I have someone to trade with. Plus it helps to screw up my opponents' economies.)
It is advisable to race to the trade nodes around the southern end of Japan before any others get there. If one gets taken before you can get there, park a ship next to them, then spam their owners with rebellions until they die. Try to take the other two trade nodes in the same way if you can, especially the iron trade in the far north - it is the only resource not available on/around the two southern islands, so if you take it you won't have to depend on others to build whatever you want.