Cocoa nibs are probably de rigueur
for chocolate stouts. Consider adding a small amount of vanilla bean to round out the chocolate flavor.
Those carolina reapers are probably too spicy for the amount of flavor you need to extract. I can't see how you'll get enough flavor to justify the heat. I'd opt for the ancho or preferably try to source dried guajillo and use those or guajillo in combination with ancho and possibly the smallest sliver of a reaper if you want it in there.
My favorite beer in this style comes from a small brewpub in Denver. It's actually what gets called a mole stout so it has cinnamon in it but you could easily omit it. Take a peak at the recipe here: https://beerandbrewing.com/VlOCax8AAFANy3x6/article/copper-kettle-mexican-chocolate-stout-recipe