(last updated 17.2.2018)
I believe priest is not only a support class but should be strong enough to solo dungeons and make good scores in spire.
You will need int and cons stats in your gear and cast time is extremely important as you will cast your heals and skills faster.
According to this I will tell you what I look for in gear, doesn't matter the type or lvl.
My priority is intelligent in random stats in all pieces. When you look in an item, first 2 or 3 stats are changing according to different items and you can refine (change) those stats.But last 2 or 3 stats you see are fixed. No matter what you do, you can't change them.They are good for your class.
To me in a perfect item i desire for intelligent in : Hat , Armor , Boots ,Scepter.
I look for %cast time at Pauldron.
If I haven't capped my critical rate yet i look for % magic crit rate on Gloves.
I look for % magic attack on crest and necklace.
For rings i look for %hp or % cast time.
For crossbow, if i want more cast time i look for it also if i haven't capped my crit rate i look for % crit rate.
I don't use lance at all, maybe when lvling and solo things.You can get magic atk at lance.
As gem I use %magic atk on my bracelet.
Be aware! When you are on mount, the dps on your scepter won't matter, the dps on your crossbow and lance will matter.This so important when you wanna do Trauna and Attaius.
What I use as seal:
For Heroic seals I go for familiars that give Int and all stat. (Caspert,Kargyle,Poyo,Elicuno,Nebes)
For Legendaries I go for Seals that give ,Magic Atk, Magic Crit DMG Overall atk, Overall crit DMG, All stats , HP (Mix rodesh seals with graveons or runelon but when you feel comfortable with hp just seal more rodesh--> updated seals are Aidus,Radan or Benotien for dps , Tishanan for hp, but Runelon is still good it gives stat limit break for you.)
In dungeons as pet, to improve my cast time ans m.atk i use abagne ( or use frost its gives %hp and cast time).If I solo, collection pets can help you as they give %atk, %hp % def and % move speed.(Rondo, Mercuris,Yorminsul)
I also look for %atk and %hp familiars as mount.(Hameon, Torkai etc.)
If you worried about your hp, don't forget all stat will count as constitution and if you have %hp rings you won't have problem at all.Also tempering your gear to +15 will help you a lot.And try to temper your weapon max.( If you will do scarlet try to temper your gear more than +15, you will need lots of defence and hp there)
Try to get your cooldown and magic crit rate to max.And get as high as cast time and int possible.( you can use rabbit steak from shady warrens for more cast time )
I hope this guide will help you in dungeons and spire.Feel free to ask me any questions in game or discord. SydolinEmuna#7426