2. I think that it depends on just how well the lid fits. You don't need as much humidity for the casings, but if your lid doesn't hold enough humidity you could have problems.

3. Cakes are all a little diffrent. They colonize at diffrent rates, and pin diffrently as well. If you birth a cake after 100% you may wait about a week depending on what type of shrooms you are growing. If you are using PF than it is usually better to wait until you see pins in the jars before you birth.