Start with electrical requirements, then check datasheet limits, thermal behavior, availability, safety margin and compatibility with your project.
Cheap modules can work for prototypes, but you should verify real current rating, heat, protection features, documentation and long-term reliability.
Yes. Use related calculators to estimate current, voltage drop, power loss, heat, range or runtime before selecting parts.
Runtime can be lower because of regulator losses, battery voltage sag, temperature, cutoff voltage, aging and peak current demand.
Average current is usually the most important value for runtime, especially in sleep-heavy IoT devices.