Glad you are going to use Ipe. be wary of side fixing using plastic clips for obvious reasons, Ipe clip extreme and stainless clips are best.
Cupping will always happen but much less on narrower boards up to 100mm.
With respect to Ipe and its specific density, pretty much nothing will soak in to it, hence the oiling operation I advised earlier. You can certainly use the oil on the ends or a proprietary wax based product. In my experience the wax crumbles in the winter and peels away in the summer, especially when the moisture gets behind it.