Seems kind of hard to plan for with our currently limited knowledge. I'm cool with winging it till we get there, see the number/type of enemies, map layout, etc.
And I'd kinda rather Orsik hold onto those spell slots. A Faerie Fire would be nice when the fight starts, though.
I'll be honest and say I don't think Erevan should up front as the sacrifice. You're dangerous...but squishy. -_-;; Are you sure you wanna do that? Surana is built to take damage. That's...kinda all she does. But if you really want to, ¯\_(ツ)_/¯