Brett L. won't necessarily make your beer sour. I do prefer WY Brett L. vs WL Brett L. The WY strain lends a nice tart cherry note to the beer while the WL strain is more horsey, goaty, and sweaty/slightly smokey (more traditional farmyard brett).
As per IBU's, I probably wouldn't go over 20 based on your grain bill. Maybe even 15 if you really want the fruit to shine through. As per hop selection, I agree with Jim. Something earthy/spicey/floral would pair nicely with the fruit and saison yeast. Think EKG, Willamette, Saaz, Hallertau, etc.