Is possible to add more than 4 images?

I would think so. Just copy all the code with 'image4' and make it 'image5'

I tried but it didnt work, it adds a fifth miniview but once you click it, it redirects you to the first image, not sure why

You edited the css too?

No, Im not sure what should I change in the css

I can't say for sure, but probably this code:

.gallery input#image4:checked ~ .wrap figure {
  -webkit-transform: translateX(-300%);
          transform: translateX(-300%);
}
.gallery input#image4:checked ~ .wrap figure:not(:nth-of-type(4)) {
  opacity: 0;
}
.gallery input#image4:checked ~ .thumbnails .slider {
  -webkit-transform: translateY(300%);
          transform: translateY(300%);
}
.gallery input#image4:checked ~ .thumbnails .thumb:nth-of-type(4) {
  opacity: 1;
  cursor: default;
}

copy that and change all the image4's to image5 to correspond to the html.

Nice man! Thanks, it worked, only one more thing you must do is to change the 300% to 400% and works just fine!