If I have already created an App, but then want to add Tabs, is it better to do this through the App Designer interface or "programmatically"? Any hints to expedite the process?

That is, there is code existing already, so if I add "Tabs", how do I get my existing code into the Tab of my choice?

1. Should I (for example...) start an entirely new App and begin with Tabs? Or
2. Add Tabs to my existing App using the App Designer interface, and rearrange the existing App code into the tabs? Or,
3. Add tabs _ programmatically,_ and put the new Tab code so as to encompass the existing code that I want on that Tab?
4. Other ???