Whats the most effective way to structure a power training plan on the StagesBike SB20, and are there specific zones or intensities that should be prioritized for overall cycling fitness gains? For example, should I be focusing on building my Functional Threshold Power (FTP) through high-intensity interval workouts, or would I see greater overall benefits from spending more time in the endurance zone? Are there any specific cadence or gear ratio considerations that should be taken into account when designing a training plan on a smart bike like the SB20, and how can I ensure that my indoor training is translating to improved performance on the road or trail?