That's an open ended question. It completely depends on how much power you want to make. If you leave the stock turbo on, you'll never have to do anything to the DET. People have made over 400 wheel HP on stock DE motors, never mind DETs which can handle a bit more.
If you're going to tear your motor apart, I'd say just replace the bearings while you're in there, and look for wear on anything else and replace it if it looks worn.