If I buy a skin piece with Iridescent shards, will I get a discount for outfit as Auric cells?

If I'm correct in what you're asking, you will still get a 10% discount on just 2 outfit pieces, however the actual discount value will be less than if you bought all 3 pieces with cells as 10% of 800 is obviously less than 10% of 1200.

i personally don't think you should spend money on skins when there are a ton of killers and survivors to buy. unless you're buying the legendary skins or event exclusice ones. in which case those are cool. the base skins aren't worth investing shards into. but if you truly don't want to buy characters then...

yes i think so 🤷🏻‍♂️ roughly. but not sure since i don't know what outfit you're referring to