Depends on how you feel,would you be satisfied with just three or are to interested in more?Its not going to be stressful at all really because the birds will be able to see each other for so long.Once added they will all probably look as if they have been together for years,maybe a few pecks...
Integrating at a young age is a great idea.Keeping then separated for the first few weeks is a good idea.By four months I would add them together.I seriously doubt you will have any serious issues.Tehre might be a fight or two or nine at all but I wouldn’t worry.