Magento – Duplicate images for associated simple items within a configurable product

I had the same issue and here is what I've used. It's a 'quick and dirty' script that works with the database directly, so back up you DB before trying it. Also add the table prefix if you have one.

$resource = Mage::getSingleton('core/resource');
$attributes = array('image', 'thumbnail', 'small_image');
$connection = $resource->getConnection('core_write');
$collection = Mage::getModel('catalog/product')->getCollection()
    ->addAttributeToSelect($attributes)
    ->addAttributeToFilter('type_id', 'configurable')
    ->setOrder('sku', 'ASC');

foreach($collection as $product){
    //$product->load($product->getId());//not sure if this is needed
    $simpleProductsIds = $product->getTypeInstance()->getUsedProductIds();
    $q = "SELECT * FROM catalog_product_entity_media_gallery WHERE entity_id = {$product->getId()}";
    $result = $connection->query($q)->fetchAll();
    foreach ($result as $row){
        $q = "SELECT * FROM catalog_product_entity_media_gallery_value where value_id = {$row['value_id']}";
        $valueResult = $connection->query($q)->fetchAll();
        foreach ($simpleProductsIds as $id){
            $q = "INSERT INTO catalog_product_entity_media_gallery SET
                attribute_id= {$row['attribute_id']},
                entity_id = {$id},
                value = '{$row['value']}'
            ";
            $connection->query($q);
            $lastInsert = $connection->lastInsertId();
            foreach ($valueResult as $val){
                $q = "INSERT INTO catalog_product_entity_media_gallery_value SET
                    value_id = {$lastInsert},
                    store_id = {$val['store_id']},
                    label = '{$val['label']}',
                    position = {$val['position']},
                    disabled = {$val['disabled']}
                ";
                $connection->query($q);
            }
        }
    }
    //update media images
    $data = array();
    foreach ($attributes as $attribute){
        $data[$attribute] = $product->getData($attribute);
    }
    Mage::getSingleton('catalog/product_action')
        ->updateAttributes($simpleProductsIds, $data, 0);
    echo "Done with product: ".$product->getId()."<br />";
}

It took about 20 seconds for 80 configurable products and about 400 simple products associated to configurable.
If you have 20k products I don't think it's a good idea to iterate the product collection like I did. You can use Mage::getSingleton('core/resource_iterator'). More about it here.

Here is an idea.
In order to have something preselected for a configurable product you must rewrite Mage_Catalog_Block_Product_View_Type_Configurable::getJsonConfig.
More exactly this part.

    $preconfiguredFlag = $currentProduct->hasPreconfiguredValues();
    if ($preconfiguredFlag) {
        $preconfiguredValues = $currentProduct->getPreconfiguredValues();
        $defaultValues       = array();
    }

Or this part

        if ($preconfiguredFlag) {
            $configValue = $preconfiguredValues->getData('super_attribute/' . $attributeId);
            if ($configValue) {
                $defaultValues[$attributeId] = $configValue;
            }
        }

You can add your custom logic around these lines of code.
I would go with this approach.
If after executing the code above defaultValues is an empty array add your logic. If it's not empty it means that the use clicked on the 'edit' button from the cart and you shouldn't interfere with that.

Now the second part.
How to get the minimum price.
Here is an explanation about how to get the min and max price from the configurable product combinations.

Other than this, I can recommend you this extension. Among other features it allows you to set from the backend the default configuration for a configurable product just by selecting a simple product associated to the configurable one.
The downside of it is that you have to edit every configurable product to set this.