That sounds like a fun project. From what I understand, the most warping is going to happen right away when you cut it into smaller pieces. I’m assuming it was kiln dried, because almost all is. There’s some interesting info about it in this video:
I think the one on the left would have better looking grain if you cut it horizontally, but that may be my opinion. If you cut it vertically, it will just be a bunch of parallel lines. But I would guess it’s more likely to warp if you cut it horizontally… The one on the right is the same either way.