Act as a senior full-stack developer with 5+ years of experience in building weather applications. Guide me step-by-step in creating a [REACT/NODE.JS] weather app using the [OPENWEATHERMAP/WEATHERAPI] public API. Include how to fetch real-time weather data for [CITY/COORDINATES], display it in a user-friendly UI with temperature, humidity, and wind speed, and handle errors like API limits or invalid locations. Provide code snippets for key functionalities and best practices for optimizing API calls and caching data. Also, suggest ways to add features like 5-day forecasts or weather icons based on conditions.