Good way to store content and settings for an RSS plugin

1. Add a Custom Post Type called 'feed'
2. Add a Custom Taxonomy for ‘feed’ called 'feed_category'
3. As you mentioned, use a Custom Post Type for your feed items, for example 'feed_item'
4. When adding an 'feed_item', add post_meta which makes the link between 'feed' and 'feed_item'. For example update_post_meta( $item_id, 'feed', $feed_id );

Your loop can be used perfectly when using my suggested structure. At step 3 you query all posts with post meta 'feed_id' = $feed_id.

Codex Links:

• Post Types
• register_post_type()
• Taxonomies
• register_taxonomy()

To get the feed items use the following code:

$category_id = 123;

$the_query = new WP_Query( array(
    'post_type' => 'feed',
    'feed_category' => $category_id
) );

$items = array();

while ( $the_query->have_posts() ) : $the_query->the_post();
    $feed_items = get_posts( array(
        'post_type' => 'feed_item',
        'meta_key' => 'feed_id',
        'meta_value' => $post->ID,
        'numberposts' => -1
    ) );

    $items = array_merge( $items, $feed_items );
endwhile;

wp_reset_postdata();

// now $items contains your feed items from the feeds in the feed_category with id 123