I would need to know more about who you are and your tastes, plus the flavor of the home. What you like and don't like about your home. Whatever we do in design to make over a room, affects other spaces. Our senses and reaction to color, textures and personal design taste plays a part in decisions.

I think the FP is quite striking and you'd lose the interest of the brick pattern if it were all one color. Consider putting doors on the bottom of each side so it isn't a wall of dark holes. I think the visual "weight" of the built-ins stands up well to the heft of the FP. If you do paint them white, I think you'll want to add some color to the backs of them or it will just become another big white wall. Here's the German Smear technique which would allow some of the color variation to still be seen.

Big white wall

Transitional Living Room · More Info

German Smear

German Schmear on two story brick fireplace · More Info

Could look like this

Went ahead and painted cabinets. Looks alot better now. What should I do with the middle wood mantle?

Looks great! Maybe white-wash the Mantel. I think it might be a softer blend... than a solid white to tie the brick and shelving together.

Solid white might become too focal, especially since it is visually broken by brick on each side.

It will also add another texture to the entire unit.

Similar to this, allowing some original color to show through.

You could also leave it as is ... if you have similar wood tones in your other furnishings to give it a purpose which will unify the colors in the room.

You do not suffer a lack of shelves. I would take the mantel down and not replace it.