Hey James. Yes, you can create a Slice for nested content and for creating a column and have one of the fields select another slice as a child using Content Relationship fields.
To achieve this, you can follow these steps:
Create a Slice for the parent component, in this case, the column. This Slice will contain the Content Relationship field that will allow you to select the child component.
Create a Slice for the Custom Type that'll be the child component, in this case you'd use a rich text block or image.
When you create a new document, select the parent Slice and choose the child Document with the 'child component' Slice from the Content Relationship field.
Repeat this process for each column in that you want to have child components.
Using Content Relationship fields, you can create complex components with child components that content editors can select and add. This allows for greater flexibility and customization of your content.
Yes, Custom Types are designed for modeling pages. Content Relationship fields help you link content from one document to another. And you can add this field inside or outside Slices. I mentioned Slices because it's a good practice to think of Slices as components in your app.
So you could also select a Content relationship field at the top level of your Custom Type and then link the document you need from there. Can you tell me more details about your use case? What content do you need to showcase, do you have a visual example?