These are really nice looking pieces, and they reflect a coherent style. My thought is that you might get more mileage out of your fall dress if it had sleeves that could layer more easily under jackets or cardigans. OR, instead of the long cardigan, consider a vest, which would more easily pair with the fun sleeves you have chosen.
I would go with the cargos and not the leggings, if you were trying to pare down; I think they would be more versatile as they can stand on their own more, plus the solid is easier to combine in outfits than the plaid, probably. However, a wild card like plaid leggings is a really fun idea, and they are worthwhile for livening up your fall choices.
I can see how mule loafers might not be that practical in Seattle. But I don't know that they would be any less wearable than a lot of flats. Maybe you wouldn't want them on the wettest days, but we don't usually have really sloppy rain. Personally, I trade shoes for booties around mid- to late-October anyway.
p.s. On your screen name, while I've read your explanation that it comes from your cat, "Fat Henry," I persist in reading it as "fath-en-ry" and think of it as some obscure, British name or term, something from English nobility.