Yes.
You start the process prior to boarding, but the last step is completed on board when you report to your Muster station to check in. It's really easy peasy. 😊
Yes.
From the X website:
Does celebrity enforce dress code?
Shorts and flip-flops are not allowed in the evening hours. The dress code will be enforced at all restaurants. And guests are asked to follow the Smart Casual dress code in the Celebrity Theater for all evening performances.