5-10% of a 2TB drive would be 100-200 GB, which would in my opinion be plenty. But it really does depend what you're doing with it. If data isn't constantly changing, you're not moving a lot of data around, and you're just adding stuff incrementally to it, you're OK.
I'd probably buy a new drive myself right now, but it isn't critical. If you waited a couple of months, nothing bad would happen.