Let’s see here… Medium’s comment format makes it difficult to read all of these haha.

If your sidebar is a typical sidebar to the right of the text, it should appear sequentially below the main content on mobile. So scrolling down on mobile you should have header, main content, sidebar, footer. I’m not really sure what you mean by “background sidebars” though.

For your second question, yes, generally speaking you have two options; to make a single web page that is responsive (i.e. will automatically resize itself according to the device you’re using) or to have a “desktop version” and a “mobile version”. I would personally recommend the first option, it might take a little more work but it can save you a hassle in the long run. Also, most website builders and CMS themes are easy to make responsive (actually most are responsive out of the box).

There are a number of options but since you’re on a WordPress.com site I don’t know offhand what to recommend, it’s not nearly as flexible as WordPress.org from what I know.

Since you’re not especially tech savvy the easiest thing to do might be to use a different theme that IS responsive out of the box, and include your images in the main content of the post rather than in sidebars. As I mentioned before sidebars are displayed separately from the main content on mobile, so they would lose the context they have on desktop.