Bricks, Masonry, Asphalt and Concrete - Bookcase built into wall

Hello everyone, here is my situation. I want to remove the wainscotting from my wall at the bottom, and build a bookcase into the wall approx. 30"H x 8'L x 13-14" deep. The wall I want to cut into is on the first floor, about 15" thick, and is a wall where the original house, and an addition come together. Since the rest of the house is brick, i would guess that the inside of this wall is probably mostly, or all brick also.

I'm sure it must be a load bearing wall... what would be the proper way to support it, if it does indeed need to be supported while installing a prebuilt bookcase of my own making. Would I even need to support the wall, if I made the bookcase in 2/ 4 foot sections, and only removed that much of the wall at one time? Do I need to add a header above it? 10@ 2x10s nailed together? Any help would be most appreciated. Thank you !!!

Start by hiring an engineer to do load calculations and size the lintel. Hiring a masonry contractor to make the modifications would be a wise decision also. This is not a small project.