There is a basic website (homepage and 5 subpages) with static content, we want to add something like a slideshow of current offers with custom images that would change every month. We also want to include an image gallery with effects like Lightbox.The person who is going to add/modify/delete the images in the two new modules doesn't want to deal with FTP. According to your experience, should we install a CMS (Joomla/Drupal) for this or just create a our own basic image management system to upload/select/delete the images?
CMS vs homebrew system for implementing an image slideshow
architecture;development approach
Due to the simple nature of your site and the limited CMS-type needs, I would not implement a full CMS and just create a simple, upload/modify/delete page for the monthly offers.If you plan or expect more CMS-type activities to begin taking place in the future you might want to consider setting up a CMS though.Also consider that training the user. Your custom built offer-updater would most likely be much simpler for the end-user, less complexity.  EditImplementing a full CMS would most likely take a good bit more time to setup raising the cost to your client/company.