A: Generally, humidors operate best at 2/3rds capacity. You just need to be sure not to over-humidify. The units that come with your humidor were designed to humidify up to the capacity. If you are using crystals this becomes less of a concern due to thier ability to absorb moisture.
A: With a desktop humidor such as this, some people don't even bother with rotating. Merely because smaller humidors are easier to keep more evenly humidified ( it is a much smaller amount of space compared to a large cabinet, where 'pockets' can form). But, I always advise it regardless of size. Every 3-4 weeks I would change things up.