You can add this CSS:

div.wp-caption {
    background: none;
}

How do I make white or transparent the captioned picture frame?

This post below shows well the issue:
http://limetreefruits.com/2012/10/02/desperate-need-of-organizational-help/

Thanks a bunch!

Thank you thou!

And why would say this solution is not recommended?

Because it limits you to needing to change the CSS if any of the heights of the widgets you moved to the left are changed. So as long as you understand the dependency and learn how to work with the CSS, you should be okay.

Can I pull both outside columns further out so the main post page can be wider?

You would need to first make the container element for the content and sidebar items wider. Her's how:

#main .wrap {
	width: 1220px;
}

Then find the ".content-sidebar #content, .layout-default #content" rule in your custom CSS and increase the width by the same amount that you increased the container (or wrapper) width. In this case, the "@main .wrap" was set to 1020px, so if you increased it to 1220px like my example above, then you'd want to add 200px to the #content (main column). Make sure to match the limit width value on your Appearance → Custom Design → CSS page to match the main column width you choose.

For the three columns thing, can I pull both outside columns further out so the main post page can be wider?
And why would say this solution is not recommended? :)

Thanks!

I would add a text-widget on the right sidebar with buttons I create and link to the pages. But then, how do I publish the pages without them showing up on the default menu bar?

If you use a custom menu, only the items you add will show up in the main menu and other pages you create won't show unless you add them specifically. See http://en.support.wordpress.com/menus/

I would recommend this solution over the first one.

Is that a way to push all two columns further to the right and add a third sidebar to the left with the menu buttons and/or text-widgets? That would be my preferred solution.

There is not a way to do this with CSS only, however, you can push already-existing content around on the page. For example, you could select specific widgets from the right, make some space on the left, and re-position some of the widgets to move them over.

There is a drawback to this solution, and that is that you can only use fixed height widgets on the left or the widgets will overlap each other when their height changes.

Here is an example to show you how a solution like this would work:

.content-sidebar #sidebar-primary,
.layout-default #sidebar-primary {
	width: 200px;
}

.content-sidebar #content,
.layout-default #content {
	width: 595px;
	padding-left: 210px;
}

.contain {
	position: relative;
}

#search-2 {
	width: 170px;
	position: absolute;
	top: 45px;
	left: 0;
}

#text-12 {
	width: 180px;
	position: absolute;
	top: 165px;
	left: 0;
}

Note that this example is very specific to your site. It uses widget ID values "search-2" and "text-12." Each time you add a new widget, it gets a unique ID. You need to add the widget and then look in the page source to find out what it's ID is and then use that in the CSS to move it where you want in the layout.

how can I make the main post column wider?

To make the main post column wider and the sidebar smaller, add this to your Appearance → Custom Design → CSS editor:

.content-sidebar #sidebar-primary,
.layout-default #sidebar-primary {
	width: 225px;
}

.content-sidebar #content,
.layout-default #content {
	width: 770px;
}

You should also update the limit width value at the bottom of the Appearance → Custom Design → CSS page to match the main content area width, so 770 in this case.

Thanks in advance!

I am starting to add pages to my blog but didn't want the menu to show up right at the top under the banner.
Is that a way to push all two columns further to the right and add a third sidebar to the left with the menu buttons and/or text-widgets? That would be my preferred solution.
If not possible, I would add a text-widget on the right sidebar with buttons I create and link to the pages. But then, how do I publish the pages without them showing up on the default menu bar?

Thank you!

And here's a beginner's CSS tutorial which I'd also recommend checking out:
http://www.htmldog.com/guides/cssbeginner/

For the font-size though, there is one tricky thing in your case. Because you have already changed the font settings for the body text on the Appearance → Custom Design → Fonts page, you must add an "!important" rule to the end of the font-size property. So, to make the entire byline larger, find the "div.byline" set in your custom CSS and add this:

font-size: 18px !important;

Adjust the number as necessary.

To target just the comment link, you could do something like this but note that it uses CSS3 which is new and only works in the latest browsers:

.byline [title^="Comment"] {
	font-size: 18px !important;
}

Adjust the number as necessary.

#site-title {
	display: block;
}

#branding #site-title a {
	display: block;
	width:1055px;
	height:229px;
	text-indent: -9999px;
	text-alignment: left;
}

If I can't change the font style is that a way to make the font bigger and/or bold? My point is just to have the comments (and the rest of the line if need be) to stand out a little bit more. You can barely tell it is there.

(I tried to invent a code like "font-size" something but of course didn't work! :D )

div.byline {
	position: absolute;
	bottom: 10px;
	width: 97%;
}
.hentry {
	padding-bottom: 20px;
}

Regarding the font, ah, I've just realized that the byline is part of the body text and so the font for the comments link and the body text (which is set to FF Dagny) already match.

No worries about the separate topics. I'm glad you asked about it! Plus it's good because other people may see the advice and post separate topics too.

Yes, please! I want both, to move everything down at the bottom of the posts and change fonts. Preferably change the font just for the comments.

And I will post in separate topics next time, sorry about that!

4-If the comments are below the post, how can I make it the same font as the posts title (snicker)?

Do you still want to do this one even if you can't move just the comments link to the bottom of posts?

3-How can I put the comments and the edit link at the bottom of the post leaving the date on top?

In the Retro-fitted theme, there's no simple way to grab onto just one of the byline links such as the comments link only. The edit link would be easier, but that link is only seen by logged in users of the blog with rights to edit, so I wouldn't bother with it at all even (unless it really really bothers you or something).