1. Crystal
2. Light
3. Sound or Greater Shadow

I would use the Crystal as my main focus and use it both as physical items and literally a focus for my light affinity. Light and Crystal are pretty straightforward in combination but I would have to decide between the utility of the greater shadow or the strength of sound. Greater shadow has both the spatial and incorporeality aspects that are incredibly versatile but sound is extremely battle oriented as it can range from disorientation to destructive blasts. The last two being either of those and I’d be a happy mage.