Hello all! We are in the process of deciding on the final design of the fireplace in our great room and I'm in need of advice!

The current plan is to put ledgestone on all three sides of the fireplace up to the mantel and then drywall above that with the ceiling being 18' high in that room. The TV will go above the mantel on the drywalled part. We originally envisioned stone all the way up but that's not going to happen at this point. Anyway, the question has to do with the built-in cabinets/shelves that we would like to install on both sides of the fireplace. They won't actually be "built-in" but rather bookcase style pieces that will be ordered from a cabinet company with doors on the bottom and open shelving on top. The options we are looking at are 84" high units that are either 12" or 21" deep.The fireplace box is 24" deep. The concern is how to go about placing stone on the side of the fireplace with the cabinets being there. Since the cabinets will be higher than the mantel, would it look bad to have stone meet up with the cabinets to the point where the mantel is and then drywall from there? We have been told that we should just do stone on the front face of the fireplace and it would be drywall on the sides. I think only having stone on the front would cheapen the overall look of the fireplace and really want to figure out a way to have it on the sides as well. I'm just not sure how to do it! Also, any thoughts on whether we should go with the 12" or 21" deep cabinets? Thanks in advance!