Expanding dimensions of Black-Letterhead

I am using the Black-Letterhead theme for my blog, found at https://www.ilovehorror.net. Basically, I’d like to know how to do the following:

1. I’d like to increase the dimensions of the overall content portion of the theme. For example, the black against the grey would be expanded to be wider.

2. If (1) is achievable, I’d like the placement of the text to remain the same (still justified on the far left) and increase the size of the right sidebar.

3. If THOSE are all feasible, is there a widget, or a plugin, or a CSS code that would allow certain sections of the sidebar to be updated with the most recent posts associated with certain tags.

I’m aware this is a lot of requests, and all I really need is to be pointed in the right direction. Thanks so much in advance.