it will be good to support two columns

In order to do this, I think we'd need to rearrange our configuration forms. Form Builder really only works well in the current arrangement because there's room for the form below the field.

Anyway, I think handling layout would be nice to have, but I'm not sure how to actually handle it.

Maybe you can split in two steps, one to add the fields, another to configure the layout.

This is a dup of #1553314: Two/Multiple column form layout. Neither issue has many comments so I'm closing this one because it came after the first one.