vital wheat gluten percentage

If I'm making a yeast bread without wheat, for example half oat flour and half millet four (a random choice), what percentage vital wheat gluten is needed?  Also, would a different percentage be used if I was making a quick bread with baking powder?

I'm also wondering if vital wheat gluten will give a better texture and/or flavor compared to the witches brew of xanthan and other gums, gelatins, and hydrocollodials used in gluten free recipes.

I'd like to try making some wheat free breads, simply because the wheat flavor tends to dominate when it's used with other flours.

Thanks.