+Healing vs +Spirit, Down-ranking spells

I'm a newb, dungeon leveling a Priest (lvl 53, disc/holy, classic fresh) as a healer and am wondering if it's better to chase healing gear or spirit gear. I've found a couple of nice healing items in BRD, but want to make sure I'm not sacrificing too much int or spirit by equipping.

Additionally, I've heard a bit about down ranking my healing spells, watched videos etc, but I can't understand why it's preferential to spam weaker spells.

Thank you in advance for any help!