1) I'm not sure what center section you are talking about. If it is the home page, then it is full width already.
2) You can adjust the width of the sidebars, if you are very knowledgeable in css and the theme. The theme is carefully constructed so that it is responsive and shows well on all devices. To start playing with widths requires a lot of time and experience.
3) This theme only offers one sidebar.
4)I have a blog on my site on setting up a child theme. If you are wanting to change background colors, it is best to do it through a child theme. Again, to make significant changes requires pretty good knowledge of css and html.
5) Yes you can, through css.
inventorgeorge, there are already a ton of options for this theme, and I cannot help everyone extensively modify Expressions. I am certainly willing to answer the odd question or two. If you need to make extensive revisions, and you do not have the knowledge to do so, I would advise you to seek a web designer to help you.
I do not have a Pro Version of the Theme.
If you would like to continue learning I would suggest you use the Firefox browser and add a developers plugin (free) called Firebug. It is an excellent tool for looking at css and html as it is presented on the page. It will allow you to quickly detect where to go to change the css for what you want, it even lets you modify the css on the page you are looking at to see if you are correct.
Finally if you need to make significant changes, perhaps Expressions is not the theme for you! There are many excellent themes at WordPress.org, and perhaps you will find one that fits your requirements without significant modifications.