There is no current way to display more quests on the quest preview plate than 5. You are not missing a setting to show more there just isn't one. You can go into then journal and mark up to 5 you want prioritized to show, or utilize the sugested duties pop up which can be found in the character> gameplay settings. This will only show you names, no progression information, it will also display level appropriate fate in the area you are in, and any level appropriate dungeons.