Sorry, that is not possible with the recent posts section in the customizer.
You could use a plugin that has options to display your posts in various formats, and use the plugin in the page content of your homepage (or any page).
The CoBlocks plugin has a Posts block which you can use to display your posts.
For example you could add a Posts block with posts from Category A in 3 columns, and then add a Posts block from Category B in 4 columns etc.
There are also many other plugins dedicated to displaying blog posts, too many to list here. I would recommend trying out a few of them to find one you like.