Luckily or sadly (depending on how you see it) most cosmetic armor from the gem store are outfits and not separate pieces which can be mixed and matched. None of my 18 characters is wearing an outfit and none wears a complete set of a particular armor.
Same. Outfits are pretty boring (not visually - some of them are really good-looking), I actually enjoy customizing the looks of my characters.
I do wear outfits sometimes, mostly when I'm not done with gearing the character, it's low level or I need to unlock some skins first to complete the look.
Otherwise, I just wear my custom mix of skins.