I'm speaking from experience.
My in-town flock a number of years ago was mixed so when I moved to this property I got a mixed flock. But then I fell in love with the Blue Australorps that I'd gotten because the Delawares I'd gone for didn't come in and it was already late in the summer for...
I suggest adding chicks next year. There are many advantages to a multi-age flock that I'm discovering now in my 3rd year on this property.
Among others, after having chickens for a year you might find that you really LOVE a specific breed and want to focus on them.