Custom PCB design — equine field sensor (nRF52840, IMU, GPS, LoRa, optional ECG)

Hi there, I'm developing a wearable sensor device for horses, primarily for extended field data-collection in Argentina, with live telemetry. I have a working prototype (IMU + GPS + SD logging on battery) and need it engineered onto a compact, low-power custom PCB. I want a designer who will advise on component selection against the requirements below — not just execute a fixed list. I can share the current component list, working firmware, and prototype photos. Functional requirements: MCU: low-power (Nordic nRF52840 preferred, or your recommendation vs ESP32-S3) IMU: 6-axis, must accurately capture stride/gait dynamics at ~70–100 Hz (currently BMI270; advise if better suited) GPS: u-blox MAX-M10S class (I²C), with antenna provision LoRa: long-range, low-bandwidth telemetry (position/status only — NOT the high-rate IMU stream). 915 MHz band for Argentina is the priority build; please also support an 868 MHz (UK/EU) variant from the same layout if feasible Storage: microSD (SPI) for full-resolution local logging Optional ECG front-end: provision for heart-rate sensing (AD8232 or your recommended AFE) + electrode connector — capability required; I understand real-world ECG on a moving horse is unproven/exploratory Power: LiPo + USB-C charging + battery-level monitoring; power switch + status LED Build configurations from ONE design (please advise if you'd structure differently): Regional: 915 MHz (Argentina, priority) and 868 MHz (UK/EU) LoRa variants from the same base layout ECG: an optional front-end that can be populated (HR unit) or depopulated (lower-cost no-HR unit) Data architecture: High-rate IMU → logged to microSD locally (and/or BLE on download) Low-rate position/status → transmitted via LoRa for live remote monitoring Design priorities (in tension — please optimise in this order unless you advise otherwise): Accurate stride/gait motion capture (data integrity is the core purpose) ~24-hour battery life in the field Small and lightweight (wearable, mounts on a moving horse) ECG sensitivity where achievable within the above I'd value your engineering judgement on the battery/size/runtime trade-off to hit ~24h at minimum weight. Reliability (this is a field-critical device): Robust, low-power, tolerant of vibration/movement on a moving horse Designed toward a rugged, eventually waterproof enclosure I intend to run multiple units for redundancy — clean, reproducible assembly matters Deliverables: Schematic PCB layout Gerber files for fabrication Bill of materials (BOM) Your component recommendations with brief rationale Notes on the size/battery/runtime trade-off Fixed-price, milestone-based (schematic → layout → final files); timeline estimate To apply, please share: Relevant portfolio (low-power wireless, wearable, GPS/LoRa, or biosensor work especially) Your recommended MCU + component approach Rough timeline and fixed-price estimate