How to Customize RSS feed

I posted in the RSS section however it seems that that area is MIA when it comes to activity.

I am using Simplepie to connect two parts of my site together. My main site is running on a CMS while I have a news section which is using wordpress.

My problem is this. To display the most recent posts on the CMS I need to use Simplepie however that only shows what is on the RSS. So I went hunting for ways to edit and customize your rss feed but it seems that most guides and tutorials are regurgitated across the net and nothing really fits what I am looking for.

I am trying to get it so that my rss feed shows the first post only along with the thumbnail and snippet. Under that I would prefer to have it display 5 links to the next posts in sequence.

Basically it would look like this

Image here – Title
written by – date
TEXT SUMMARY

link to post #2
link to post #3
link to post #4
link to post#5

How do I do this. I did find where I should be editing for this but nothing seems to provide instructions on how to change your css file, including adding the thumbnails

Here is what I have in there already

<channel>
	<title><?php bloginfo_rss('name'); wp_title_rss(); ?></title>
	<atom:link href="<?php self_link(); ?>" rel="self" type="application/rss+xml" />
	<link><?php bloginfo_rss('url') ?></link>
	<description><?php bloginfo_rss("description") ?></description>
	<pubDate><?php echo mysql2date('D, d M Y H:i:s +0000', get_lastpostmodified('GMT'), false); ?></pubDate>
	<?php the_generator( 'rss2' ); ?>
	<language><?php echo get_option('rss_language'); ?></language>
	<?php do_action('rss2_head'); ?>
	<?php while( have_posts()) : the_post(); ?>
	<item>
		<title><?php the_title_rss() ?></title>
		<link><?php the_permalink_rss() ?></link>
		<comments><?php comments_link(); ?></comments>
		<pubDate><?php echo mysql2date('D, d M Y H:i:s +0000', get_post_time('Y-m-d H:i:s', true), false); ?></pubDate>
		<dc:creator><?php the_author() ?></dc:creator>
		<?php the_category_rss() ?>

		<guid isPermaLink="false"><?php the_guid(); ?></guid>
<?php if (get_option('rss_use_excerpt')) : ?>
		<description><![CDATA[<?php the_excerpt_rss() ?>]]></description>
<?php else : ?>
		<description><![CDATA[<?php the_excerpt_rss() ?>]]></description>
	<?php if ( strlen( $post->post_content ) > 0 ) : ?>
		<content:encoded><![CDATA[<?php the_content() ?>]]></content:encoded>
	<?php else : ?>
		<content:encoded><![CDATA[<?php the_excerpt_rss() ?>]]></content:encoded>
	<?php endif; ?>
<?php endif; ?>
		<wfw:commentRss><?php echo get_post_comments_feed_link(); ?></wfw:commentRss>
<?php rss_enclosure(); ?>
	<?php do_action('rss2_item'); ?>
	</item>
	<?php endwhile; ?>
</channel>