Three images.
Each one leads to exactly one seperate site.
So the minimum of your Website is (in short)
1. Startpage (Home) … with the three pictures (and some other stuff).
2. A page as a target for the picture #1
3. A page as a target for the picture #2
4. A page as a target for the picture #3
In the Customizr-Options you can select, which page will go with 1, 2 or 3.
And the pictures you will see on your homepage later on, will be the pictures, you have defined in the page-editing for site-1, for site-2 and for site-3.
This would be the usual procedure.
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Do you want to have sites “under” the pictures?
Or do you want to have the pictures connected with something else or with nothing at all?