Looking at the URL to the page you gave above there are only about 15 or so images referenced on that page. WhyNoPadlock only checks one page at a time. The mixed content warnings you are getting (from WhyNoPadlock) are “soft” warnings and should be fixed but shouldn’t stop you from implementing the SSL.
Only active mixed content (things that change a page like Javascript or CSS) will "break a site.
I would check the other pages before working on the redirects.
The redirect isn’t working, there are literally thousands of ways to right redirects so I can give you one that works for any site (no changes needed):
RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
Just make sure you have the .htaccess file in the correct location.
As for the Warehoused images being on a separate subdomain, if you want to fix them you will need to get a certificate(these should be free nowadays) for that subdomain copy/move them to the main domain. You would still have to "change the references to them in the RW project.