I need to open "Select a category" page when the Create Document/Add Document wizards ends. ie. Similar to " Modify all properties when this wizard closes." this functionality, I need to open categories page after modify properties page.
Look at the doPostCommitProcessing() method in CreateContentWizard for how the edit properties dialog is displayed, you can use this approach to open the category page.
Unfortunately though the edit categories page is not a dialog so you'll need to do a bit of setup before calling it. You'll need to setup the node for DocumentDetailsBean, setup the node to accept categories i.e. add the cm:generalclassifiable aspect and then setup the categories for editing in DocumentDetailsBean. Finally you'll need to return the "editCategories" outcome to make the app go to the edit-categories.jsp page.
You'll need to do this in the doPostCommitProcessing() method in SetContentPropertiesDialog
I did something similar that might be suitable for you – in the "Modify properties" page of the Add Content Dialog wizard, I have users selecting categories there. This thread details how to do this: