Welcome to ProBoards! I've been using it for a long time and it's cool that others are seeing the light.
Go to Admin > Themes > Advanced Styles & CSS and the "Text Styles" in the "FORUM" section. On our forum we went the extra step and imported Google fonts, but this is a good place for you to start.
This one is a little bit harder. You'll need to go to Admin > Themes > Layout Templates and then select "Thread" and the the "Post List" tab.
You should see something that looks like this:
<div class="controls">
$[post.quote_button]
$[post.edit_button]
$[post.likes.button]
$[post.select_options]
</div>
You'll need to move that to where you want the buttons to show. A good place might be on the line directly after `<td class="foot">` and before `{if $[post.edited]}`
Once you do this, you'll notice that the buttons are on the left of the post instead of the right. This is something you can fix by directly modifying the CSS, or inline styles by editing it to be:
<div class="controls" style="float:right;">
$[post.quote_button]
$[post.edit_button]
$[post.likes.button]
$[post.select_options]
</div>
<div style="clear:both;"></div>
Notice the extra divs and styles. This will float it to the right again and makes sure things stay where they're supposed to.
Back in the "Advanced Styles & CSS" page, go down to the "Objects" section. Click "Buttons" and you'll have options to change a lot about the buttons on your forum from the colors, size, or even to add a background image.
Let's go back to Admin > Themes > Layout Templates > Thread, but this time stay on the first "Thread" tab.
Look for:
$[pagination]
This is the part listing your page numbers. You can try moving it to the bottom of this page, like maybe just above this part:
</div>
</div>
$[quick_reply]
I'm not sure you can do this. Maybe someone else knows better?
What do you mean by side bars? The gap on the sides of the content and your browser? If so, that's back in the "Advanced Styles & CSS" > FORUM > Width. This works on either pixels or percent. 90% might be good. This would be the answer to your final question as well.