The re-sizing has been around for a while now, but yes, you can do that. The theme has no image sizing to prevent that. You can insert an image any size you want into your post. The only thing Preference has is the responsiveness that an image will auto adjust in size (relative sizing) if an image is in a container that has a specific pixel dimension. As you make your browser window smaller, the image auto adjusts. Long story short, you can put any image into your post or page.
As for your other issue, it will more likely be the image tag styling that is an inline-block, but it’s been problematic actually for some. For some people it needs to be a block while others need it to be inline-block. Right now the theme is coded as:
/* Image styles */
Try doing adding custom css as display: block; and see how that works for you.