Hi Chantal
Answer question 1:
YES, select a custom thumbnailsize in the widgets dropdown and use CSS to finalise it.
Answer question 2:
Yes, Make use of a custom template inside your theme (see doc) and customise that template to your needs (include with a little bit help of CSS).
In your case the change inside the template could look like this:
<li class="<?php echo $class; ?>">
<?php if ($title_is_active && $title_is_link) : ?>
<a class="lastViewedTitle" href="<?php echo $perma; ?>"><?php echo $title; ?></a>
<?php elseif ($title_is_active && !$title_is_link) : ?>
<h3 class="lastViewedTitle"><?php echo $title; ?></h3>
<?php endif; ?>
<?php if ($hasThumb && !$thumb_is_link): ?>
<div class="lastViewedThumb"><?php echo $thumb; ?></div>
<?php elseif ($hasThumb && $thumb_is_link) : ?>
<a class="lastViewedThumb" href="<?php echo $perma; ?>"><?php echo $thumb; ?></a>
<?php endif; ?>
<div class="lastViewedcontent">
<?php if ($content_is_link && $content_is_active) : ?>
<a href="<?php echo $perma; ?>" class="lastViewedExcerpt">
<div>
<?php echo $content; ?>
<?php if ($more_active) : ?>
<span class="more"><?php echo $more_title; ?></span>
<?php endif; ?>
</div>
</a>
<?php elseif (!$content_is_link && $content_is_active) : ?>
<div class='lastViewedExcerpt'>
<?php echo $content; ?>
<?php if ($more_active) : ?>
<a href="<?php echo $perma; ?>" class="more"><?php echo $more_title; ?></a>
<?php endif; ?>
</div>
<?php endif; ?>
</div>
</li>
good luck and let me know!
Wouter