Built-In Library Shelving with Window-Seat Nook

We have an underused bay window in our living room and want to turn the whole wall into a proper reading corner. The project is two floor-to-ceiling bookcases built into the alcoves on either side of the window, joined across the top by a shallow bridging shelf, with a bench seat built into the window recess itself. We would like the carcasses made from furniture-grade birch plywood with solid poplar face frames, painted rather than stained, since the room already has warm oak flooring and we do not want competing wood tones. Shelf spacing should be adjustable on shelf pins for at least the lower two-thirds of each case, with a few fixed shelves near the top for rigidity. The window seat needs a hinged lid or two, since the deck underneath will serve as storage for blankets and board games — please plan for full-extension hinges that can hold the lid open safely without a prop stick. We would like a cushion made to the exact seat dimensions, roughly four inches thick, with a removable zippered cover in a fabric we will choose separately, plus two or three throw pillows sized to the flanking bookcases. Trim should include a simple picture-frame moulding on the face frames and a crown detail at the top that matches the existing baseboard profile in the room, which we can photograph for reference. Lighting is a nice-to-have: if it is not too disruptive, we would like low-profile LED strip lighting under the top shelf on each side, wired to a single switch near the doorway, but we are open to leaving that for a separate electrician if it complicates the carpentry timeline. The whole assembly needs to be securely anchored to the studs given the weight of a full book collection — we have roughly thirty linear feet of books to shelve, mostly hardcovers, so shelf thickness and support spacing should be sized accordingly rather than using thin veneer shelving that will sag over time. We can provide exact window and alcove measurements after the first site visit, and we are flexible on start date but would like the work substantially finished within the stated timeframe. Please include in your proposal your approach to on-site finishing versus shop-built modules, how you plan to handle the transition between the fixed shelving and the window seat structurally, and examples of similar reading-nook or library-wall builds you have completed.