Hey Chris,
both the 404 error page and the archive pages are usually not something that is created via the “Add Page” admin menu in WordPress – they appear automatically under certain conditions, e.g. an URL slug that does not refer to any existing page (in case of 404) or a query with certain parameters (in case of archive and search pages).
The 404 page does not have a custom background setting so far in Tokyo, I will consider adding this feature in the next version; meanwhile, you can alter its background via custom CSS, by setting a custom background image property for the “page-background” element e.g.
.error404 #page-background { background-image: url('images/yourimage.jpg'); }
You can read more on the “background-image” property e.g. here; the URL address I’ve used in the example tells the CSS to look in the /wp-content/themes/Tokyo/images/ folder.
In order to remove the search form from the header, please untick the “Display search box in the top section” option in the “Page Elements” tab of the Theme Options panel.
Sincerely,
Andrii / Satori Studio