I think FWH is usually computed as a 20 minute addition. I'd add as much of the hops as possible in the last 20 minutes. It would technically not be a SMASH, but you could bitter with something else if doing so allowed you to use more of the Apollo later. I'd go heavier on the late adds, maybe adding some at or soon after flameout and letting it steep before chilling. 18% is a lot of bittering potential, but that doesn't necessarily equate to a lot of flavor. I think you'll be fine with either grain; I've made beers with both that were quite good. I suppose MO might be the better of two acceptable options.
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