Build copy of index.php on draft post

The page template to modify is not index.php but one of the page templates included with your theme such as single.php. category.php, page.php, depends what your Home Page setting is, and what you have setup on the blog..If you want a custom Home Page, you set a (already created) page as your home page, create a new page template based on page.php (of default theme, templates vary by theme), and assign that template to the assigned home page in the page editor.

All this work is best done in a Child Theme (to not lose your edits on theme update)

Note: PHP cannot be included in the page editor directly.

Of course the draft page doesn’t display any posts as it is not set up as the blog page.

Is there an easy way around this?

for testing, add a line with query_posts() before the start of the loop (strictly for testing only; for real loops in page templates, the query needs to be a bit more sophisticated);

something like:

<?php query_posts('posts_per_page=5&cat=0'); ?>