Compact Rechargeable Audio Playback Board

I want to develop a compact, portable audio board that can store and play recorded voice prompts or downloaded MP3 files without relying on Bluetooth, AUX or USB streaming. After a full charge the unit should operate for roughly 5–10 hours, so an efficient power-management stage and a rechargeable Li-ion/Li-Po cell are essential.

The goal is a single board solution that integrates:
• On-board or removable storage (flash or micro-SD) for the audio files
• A simple user interface—basic play / pause / next controls and an LED battery indicator are enough
• A small class-D amplifier capable of driving an 8 Ω speaker at reasonable volume
• A protected charging circuit (USB-C preferred) and accurate battery gauge
• Form factor kept as slim and pocket-friendly as possible

Deliverables I will need:
1. Schematic, PCB layout (Gerber), and clean, annotated source files
2. Bill of materials with clear part numbers and supplier links
3. Firmware or player code ready for the chosen audio decoder/MCU
4. Assembly and quick-start documentation
5. A fully tested prototype (photos or short demo video proving 5-10 h playback on a single charge)

I am happy to discuss preferred audio decoder chips, MCU families, or any design trade-offs you suggest that improve runtime or audio clarity while keeping the board tiny.