Drop Cure to minimum 1 and get Deprotected Zone to at least Level 3. As you’re a full utility build you won’t be doing damage and thus higher levels of Cure aren’t useful to you, whereas even with no SPR investment you can still get a minimum of around 60 DEF reduction from Deprotected Zone which is pretty sweet.
Max Mass Heal and Revive. You can take points out of Sacrament if you need to; the scaling on the skill is not very good and its only real purpose is to provide an additional hit.
Depending on what your stats are, you can afford to take points out of Stone Skin as well.
Chaplain is actually designed to be more of a solo play option as Aspergillum is, after considering your other options, the main draw to using the class.
The only practical benefit Chaplain provides in party play under normal circumstances is Last Rites, which does the exact same damage as Sacrament (before the HP threshold bonus, anyways).
Capella is a trap/point dump; it’s very difficult to use properly and almost nobody even bothers with it. It’s a stationary field like Diev statues, but unlike the carvings, buff timers will continue to run while you’re inside the area, and when they expire you need to walk out of and back into the field to reapply them, which can be problematic as the area itself is fairly large. It’s just a huge hassle to play around and it puts the responsibility of buffing onto the other party members rather than the “dedicated” buffer, which hurts overall efficiency.
Paladin is only really good at C3 because you get Barrier and maximum uptime on Resist Elements, but depending on how much INT you have and whether or not you took Cleric C2, C1 can be worth getting just for Restoration.
Speaking of Cleric C2, you should probably get that. 5 Heal tiles per cast really blows, and the additional hits on Safety Zone at C2 really helps protect your party. Fade is also good. Like, really good.
Keep in mind that if you’re going Plague Doctor, Bloodletting’s constant HP drain forces your party members to consume Heal tiles at full health, making Cleric C2 even more desirable for the increased Heal tile count.
Oracle and Plague Doctor are classes that I wouldn’t really consider putting together, as one of two main draws to taking Oracle is Prophecy, which gets obsoleted by Plague Doctor’s Bloodletting. The other draw is Counter Spell, which is usually only practical in a PvP environment. If you don’t plan to PvP, and you don’t plan to do intense item hunting (even that is still pretty tedious as Resetting has a stupidly high cooldown), I wouldn’t take Oracle if you’re going to go Plague Doctor.
Oh also if you’re taking Priest all the way to C3, please consider at least 1 rank in Krivis, or be prepared to buy a lot of Daino scrolls.