Project Management...
There are two very logical reasons for having a Project Manager:
Better outcomes and peace of mind.
There is a strong correlation between the use of project management and any project's success.
When it comes to life in general, everything is great until it is not. It's those "it's not great" moments that are life's irritants. Perhaps they are much more than irritants.
The same holds true for projects. Your project is going really well until it is not. It is a rare project that does not have it's bad moments. Minimizing and perhaps even eliminating "bad moments" is made possible by utilizing project management.
Essentially, Project Management is the gathering and coordination of disciplines, knowledge, skills, and objectives into a unified team effort for the purpose of achieving an identified goal.
Engaging a qualified Project Manager is money well spent. The PM's purpose is to ensure that your interests and goals are paramount. When choosing a Project Manager, remember that it is not the project management firm that will shepherd your project, it is the individual(s) assigned to it. Interviewing that person is essential. Include that person's name in your contract.