A parenthesis needs to be done on the support and on the updates of the theme. Keep in mind that your theme will be visited and bought by a lot of people. They may find some issues or problems that you can solve or help to solve.
Reserve some extra time to collect all the bug fixes and release all the updates for the theme once in a month. This will ensure that the theme is always updated and that users can rely on your products and services.
To do this, you can collect some bugs and fix them in the current version of the theme; once fixed, repackage the files and resubmit the new ZIP file in the marketplace.
To maintain a report of the modifications you make for each version, you can create a file called changelog.txt and add all the fixes or the new features in the following manner:
Version 1.1 (September 6, 2013) - FIX: Minor Css bugs fixed - FIX: Top Cart Background fix - FIX: Responsive Menu - FIX: Fixed bug in Google font selector...