Just to make sure:
1. When casting an utility spell, I make a normal percentile roll.
2. When casting an attack spell, I use an open-ended roll.
3. Elemental spells are like physical attacks, they are open-ended.
The first item is not mentioned directly (normal percentile), but even though it is said at the beginning of the Adventuring chapter that all rolls are %, I think it would be good to write it explicitly in the spell casting section.
Same thing about elemental spells, you need to look at the Combat chapter to know that attack rolls are open-ended.