Once the contract is signed, we create and give you a Platform.sh Professional Developer project. If you already have a Platform.sh Professional project set up, it will be marked as belonging to your Enterprise plan. The Dev project functions identically to any other Platform.sh Professional development plan. (Do not try and upgrade the dev project or associate a domain name with it. That will simply result in unnecessary extra cost.)
In practice, you will do most of your development work on the Dev project. The Dev project is a container-based environment that simulates production but is distinct from it.
As soon as the Dev instance is available, go ahead and start developing! Branch, merge, and push however works for you to get your site built. Treat the
masterbranch as canonical for all data and "approved" for all code changes.