For the additional style on Jkreativ Dashboard actually it’s different with style.css file that you can find on theme editor. Because if you put your additional css on the Additional Style section on the JKreativ Dashboard, your additional css code will not lost when you’ve updating themes. But if you put your additional css code on the style.css file, those file will override with the new update file.
Yeah, because on masonry layout (Blog page) will rearrange your post order based on the height of post item. It’s a good idea to make the images thumbnail on your post item to have same size, but i think you can use normal layout in this case.