The basic idea of ikas theme development is, you create components and define what you need as input data in the editor. The editor is basically your playground, it will be shaped by what you need from the merchant. Everything the editor displays is being decided by you, the theme developer. You are basically creating a no-code environment for the merchants of your theme so that they can edit your theme using simple form elements. The more customization options you provide to the merchants, the more customizable the theme is going to become. It is up to you to decide how much customization you want to provide to the merchants.
The merchants will provide the prop values in the editor, and those values will be passed to your components by ikas, and you will only need to write UI code to display them. Every data type that you are going to use has the data or a data fetching function ready for you, so that you don't spend time on making API calls, or learning all of the ikas data models or organizing data.