Final question on licenses
Am I allowed to publish an app to the android app store and sell it for about 5$ with no license but provide the source upon request? The description will clearly state how to obtain the source code.
yes, you can do it. And also you can don't provide source code if you have no change on Qt Source codes. But if you are going to provide your app's source code you should response to every email (are another request way) within 3 years beginning from app release date.