About the 2+ notation, etc:
For fatigue, the spell costs half as much fatigue if the mage has one level higher in the primary path (the first path listed, if there are two, as e.g. FFFDD is primarily Fire) than the spell requires, one third if he has two levels, etc. If the mage has too few levels to cast the spell but does it anyway (e.g. if he's a communion slave casting a spell that only the communion master technically has the paths for) he takes much more fatigue. Using a gem can boost your effective level by one.
For AoE 2+, damage 9+, etc., it depends on the individual spell. Check out DrPraetorious' spreadsheet for specifics. Here's an attempt at a
link. If that doesn't work search for "Spell Modding Guide" in the forum search.
-Max