This build is using a 15/5 Wizard/Warmage multiclass. Here are the issues I found when testing:
1) Arcane Spell Failure while in Light Armor and using wizard spells.2) Warmage's Edge and Extra Edge do not apply to Wizard spells. I am unsure if this is intended or not, but I figured I'd be thorough since the feat doesn't have any descriptor to suggest it shouldn't work for multiclassed Warmages. Spells tested: Horrid Wilting, Acid Fog, Acid Sheath
With an int modifier of +9 and 5 warmage levels, I believe it should be a +11 extra damage on spells per spell level? I'm still iffy on the exact calculation.
Edit: I see in the writeup the spell failure is only meant for Warmage spells. Though, the writeup for Warmage's edge still indicates that it's any damage spells.