You spam Benefic 1 and it has a chance to proc Benefic 2 to always crit, when it lights up that's when you use it, ofc if hes getting hit really hard you can spam Benefic 2.

Seals you should always go for 3, The spell is had right now so its not really important, a tip is if you have 3 seals but only 2 different ones you can still get the 3rd different one if you just draw it and put it on someone. When you got the seals and divination is on cool down just minor arcana every card until divination is back up.

The stance is your choice when your solo healing, people go diurnal slot because its regen, you aspect him and then dps for speed clear. I personally use nocturnal because when your high enough level you get a spell that's the opposite stance, so I use that as my regen but also have chunky shielding, use opposite stance as your co healer as shields and regens don't stack for the basic spells only CDs. Like I said experiment with both and find what style you like for dungeon play.

1 thing I can say is the class doesn't come together until you get all your spells, this expansion added some good stuff even tho it isn't good on paper, it fits and works really well. Astro is a time healer and you will discover it in time