There are no hard and set rules regarding what percentage of items (e.g., 10%, 50%) you should manually code by hand in your sample before using the uClassify system.
We advise iteration until you do not see an improvement that justifies further coding efforts.
Once you have rebuilt the classifier 2 or 3 times, use the classifier on a set of uncoded data. Then filter by a single code at the 85%-95% level. Sample that list and code it.
If you get 90% accuracy, then you can decide if more accuracy is required.