Wordpress archives by custom field and date

Question

I have a strange situation on my hand.

I want to list my archives based on a custom field (numerical value) but also display something like a cover.

We have specific posts in different categories but with a numeric custom field, that is unique to multiple posts (something like edition number).

For every edition number i have a different number of posts and a cover image. I would like to display them with something like.

The cover (image) - number of posts - and the date of the edition.

I am able to query by custom value, but i am unable to get the date for them..

I'm not sure how i should approach this and therefore i'm asking here.

LATER EDIT:

What i'm trying to achieve is basically this:

1. Get a list of all unique meta_values for specific meta_key.
2. For each meta_value output the cover for it (this will be done based on the key)
3. For each meta_value list number of posts with a link to see them all (this will be also done based on the meta_value with something like ?meta_key=222.
4. Paginate so that the page won't get too big as i currently have ~600 unique keys..

Answer 1

This will get the posts filtered by custom field and its value based on categories.

$args = array( 'post_type'=>'post',

            'category__in'=> array(6, 7, 31), //category id

            'meta_key'=>'keys', // customfield name
                'meta_value'=>5, // customfield value
                    'posts_per_page'=>-1,
                        'number_posts'=>-1 );

$s = get_posts($args);

foreach($s as $e ) {

echo $e->ID.'<br/>';

echo $e->post_title.'<br/>';

}