Some of these questions are easy so I'll answer those first.
You can make any changes to the <hr class="translate_hr"/> line in your CSS file by adding a few lines. This will hide the line.
.translate_hr {
display: none;
}
The [Translate] button can only easily be put at the top or bottom of the "entry" div because it appears through a filter of the WordPress function called the_content. If there are more people that want the button at the top I could add it as an option. For now you can make these changes:
Find line 455
$content .= '<hr class="translate_hr" />
and change that to
$translate_block = '<hr class="translate_hr" />
Then find line 462
return $content;
and change that to
return $translate_block . $content;
There isn't really an easy way to move the button to any arbitrary location though. It would require adding a new option and php function to the plugin and then some code in your theme to call that function to display the button. Are there other plugins you know of that do this?