MC Next - Sandbox to Production

Good afternoon everyone, hope you are doing well. 

I would like to ask a few questions regarding sandboxes in MARKETING CLOUD NEXT, which came up as I started on a new project. To give you some general context, this client basically wants to do all the development in the sandbox, and once everything is validated and tested, deploy it to production—which is totally fine.

However, here are my questions: 

1 - Regarding WhatsApp: Can I perform the setup configuration, warming, and testing all within the sandbox? My concern is whether I will need to replicate this entire process in production later on. If there is an ideal scenario or best practice, I would like to understand how to proceed with this step. 

2 - Regarding Email: Similar to the WhatsApp situation, my main question is about the domain/subdomain in the sandbox. When doing all this setup, do I need to perform the IP/domain warming normally? Is it necessary to create a domain/subdomain to work in the sandbox as well, and then repeat the same step for production? Or is the process different for a sandbox? 

In short, these are my main questions, but just to reiterate: this client wants everything to be developed and tested in the sandbox, and we will only deploy to production once everything is validated.

Because of this, I have these questions so I can understand the best way to move forward. 

Thank you.