I love the image that you picked for this one and the second one, they fit together really well. They both are blue and red, with white type. The first image is much more illustrative, but they both have filled color blocks so they still work together. Having the last image be a photo doesn't really fit with the other two. THe colors of yellow and white also are different, if you want to keep this image, maybe make the type on the others yellow, and the type on the last one blue? But if you can find a nother image that matches with the others, I would do that.
I think the typeface works well with the illustrations, they are blocky and the text is blocky. The type on the first one seems really squished in the top, maybe move it to the left side? Maybe also give it a shadow? or put a thin overlay color on the image, it will still be hard to read over the lines in the clouds.
I think that the placement of the second postcard type is a little close to the eye, and the edge. It might alos need a shadow, even though the background has less disruptions.
For the last postcard, I understand why you made the type red, but even with the overlay on the image the text is hard to read. It makes sense from the quote why you want chaos, but maybe pick an image that has chaos and detail on one part of it and leaves some space open on the bottom of a corner that you can put the text uninterrupted? You will probably also need more value contrast between the type and the image.