The Oxygen theme does include a sidebar on the front page of the blog, but it could be removed with some Custom CSS. I would be glad to help with that if you decide to upgrade.
Thanks for uploading the screenshot. The Oxygen theme displays featured images called "thumbnails" above the title of each post on the blog front page, in the same height and shape, for uniformity. They are also the same width - 470 pixels - as long as the original image meets that minimum.
If the uniform featured-image thumbnails aren't to your liking, you might prefer a different theme that doesn't display featured images on the blog front page.
Just let me know if you have further questions.