When hiring a coywriter, should I stick to one writer or hire many at different times?

I have a few linked projects for which I need a copywriter to create the content for (websites, blogs and adverts). However, due to budgeting and uncertainties, I can't really plan very far in advance.

My question is; should I hire one copywriter to cover all aspects or can I hire different writers at different stages of the process? Will the content be very disjointed if it is written by different people with different styles/nuances?

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