Just finished my first game! =D

[the benevolent adversary]

congrats!
personally I sell any scroll that I do not plan to use. but I usually just cast the scrolls when I have used up my mana quotient for a battle (i.e. I plan to end every battle at full unless I am thru with an area or otherwise going to go somewhere else).
a good scroll trick is to have one of the items that allows more scrolls but not equip it until you need to buy a scroll.
so you know the rune mage can heal plants (not sure about the Cyclops though).
the other campaigns have a slightly different design. one is just boss battles the other only has 7 fights but with special arenas and acccelerated xp.