How can I use get_post_meta with add_rewrite_rule to build custom permalinks?

Not sure the rewrite rule is good, but to answer the question about getting the post meta – you already have the post Object, so you don’t need to run a function to get the global $post, which might also fail or be wrong – you can simply use:

$metaText = get_post_meta( $post->ID, 'test_text_field', true);

You will probably also want to debug the value of $metaText to ensure it returns something.