What I do for this to avoid the disruption of the mental flow of adding to the inbox is to create a task to act as the placeholder for the new project. I use a predetermined emoji in the task title to make it easily identifiable as a project placeholder.
When I am done entering tasks into the inbox, I go through and convert those placeholder tasks to projects (Edit > Convert to Project). This converts the placeholder task to a project and places it in the root of the projects list (Projects perspective). The step after that is to drag the new projects to their appropriate folder (based on areas of responsibility), one after another until all new project are placed.
If I think of the tasks for the new project when I am creating the placeholder task, I make a list of the seeding tasks in the Comments field. After there placeholder task has been converted to a project, it’s a simple matter of copying the list and pasting all the seeding tasks into the project. OmniFocus automagically converts the pasted multi-line text into individual tasks within that project.
The whole idea here is to not break your rhythm during the discovery process, so all you do is create tasks, one after the other until all are out of your brain and into your trusted system. Then apply the same batch processing method to converting the placeholder tasks into projects, one after another. Then the same for placing the new projects into their places. It’s all about the rhythm and flow.