Problem is solved! Finally i understood how frontpage custom layout effects the "full single article view", this topic made my day:
http://www.tinyportal.net/index.php?topic=33291.msg266971#msg266971Now i understand that the custom layout for a category takes effect on the view of the whole category.
For the styling of a full single article view, the frontpage custom layout is required. Imo this is a bit confusing, and its hard to find a solution if you are not very familiar with TP. But anyways, for me it works now and i bookmarked the helping topic above

If anyone else is looking for how to do an article overview with a small image (listing icon) shown next to the intro (like the layout given by "Picture + Article 2") and the full single article view without that listing icon, here are the custom code snippets that worked for me:
On the article category settings page:
<div class="tborder" style="margin-bottom: 5px;">
<div class="article windowbg" style="margin: 0pt;">
<div class="article_picturecolumn smallpad">
{article_picturecolumn}
</div>
<div class="render4 smallpad">
<h2 class="article_title">{article_title}</h2>
<div class="article_info">
{article_category}
{article_author}
{article_date}
{article_views}
{article_rating}
{article_options}
</div>
<div class="article_padding">{article_text}</div>
{article_moreauthor}
{article_bookmark}
{article_morelinks}
{article_globaltags}
{article_comments}
</div>
</div>
</div>
On the frontpage settings page:
<div class="tpcontentHeader">
<div style="margin-bottom: 5px; overflow: hidden;">
<div class="title_bar">
<h3 class="titlebg">{article_shortdate} {article_title} </h3>
</div>
<div class="windowbg2">
{article_avatar}
<div class="article_info windowbg">
{article_category}
{article_author}
{article_date}
{article_views}
{article_rating}
{article_options}
</div>
<div class="article_padding">{article_text}</div>
{article_bookmark}
{article_boardnews}
{article_moreauthor}
{article_bookmark}
{article_morelinks}
{article_globaltags}
{article_comments}
</div>
</div>
</div>
I hope, that helps someone else, too
