In "Elegant Grunge" theme, how do you activate 3-column width in CSS?& Other Q's

Here is a link to my blog. https://sharkcircle.wordpress.com/
All of the posts I have so far are just tests, testing fonts, etc., and the most recent one is a table I want to include in my first finished blog, but I haven’t put the text in around it yet.

Here are my questions. Elegant Grunge says it’s a 3-column theme (along with 1 and 2), but apparently the default is 1. Right now, the table I wrote in HTML in the top post on my blog is way too thin. So I paid for the CSS upgrade so I could change it from 1-column, which it looks like it is right now, to 3-column. I read through the whole style sheet as it is, and painstakingly tested out changing a lot of things, and nothing worked. I have been able to change the dimensions of the main post, the text (table in this instance), as in make the table wider, but I haven’t been able to make the actual column wider. So in other words, the table just runs into the sidebar, over the ‘dividing line’ between the main post and sidebar (or whatever it’s called), when what I want to do is move that dividing line line further to the right (in addition to making the whole page wider itself so as to compensate, otherwise the sidebar would run off the page, or rather get cut off). I just want the 3-column post body width like the theme said it could do, in a content – sidebar layout. Just 1 sidebar column.

So that’s my #1 question, that I can’t find an answer for anywhere on the net.

My other question, how do I change the background color/image in CSS? And not just the background around the main posts, where it still leaves the background of the post white or the default color, but actually change the background for the whole page, behind the posts included. How do I do this in CSS?

Question #3. I know you can change fonts for the text IN posts in CSS or HTML, but how do I change the font/textcolor/size/etc for post TITLES, for the date listing, for where it says “twitter updates,” for where it says “by Puckcircle,” and all of that? I don’t want to be left without control of any of the writing on my page, because the default may not go with everything else I choose.

Question #4. I designed by custom header image for a different theme, using the dimensions it specified for the custom header image, but since then I realized that theme wouldn’t work for me, so I changed to elegant grunge. Now my header image has the wrong dimensions, so I have to crop it and stretch it a little. Is there a way to change the dimensions of the custom header image the theme will take in CSS? Once I make the page itself wider, there will be room for a wider header image, so it’s not like it wouldn’t fit. It would work, if there’s a way to change it. Is there?

Question #5. If you look at the header image on my blog right now, and this would be the case no matter what size it was, it doesn’t fill up the whole top part of the blog. My image has black borders, but then outside of that is this coffee grey/black color that makes up the top part of the blog. This isn’t the header, it’s not the background color either. What is it called, and how do I change that part of the blog’s color?

Question #6. Width issues aside, my table that I wrote in HTML came out pretty nicely (by my HTML novice standards anyway), but I noticed when I previewed other themes, the table changes completely. Not just the theme around it, the colors around it, but the border width changes, sometimes the lines within the table, separating rows, disappear all together, or are only every 4 rows instead of separating each row like it’s supposed to. If I end up having to change themes as a last resort because I can’t change the width, how do I keep the table looking the same? The HTML is the exact same, it’s not like I’m taking out rows, so I don’t understand why they would disappear in other themes. But they have in some. No need to answer this as long as I don’t have to change themes, but if I do it becomes a big issue for my blog.

Those are my questions. Thank you very much! If you only have time to answer one of my questions right now, please prioritize the first one. I can’t go forward with my blog at all until I fix the column width issue. Thank you for your time and help!

(I do not know which version of wordpress I am using, only that I am using the default version for Mac, in Safari. In other words, I haven’t downloaded anything, just using it in-house on the wordpress website).