Does noindex/nofollow plus a Meta redirect stop link juice?

I believe that all of these steps will prevent Google from maintaining link juice to your new site.

If you add a robots <meta> tag to a page set to "noindex,nofollow", it will remove that page from the index and stop any flow of PageRank and other link factors. If you block a page in your robots.txt file that is already indexed, it will prevent Googlebot from crawling that page so it will also prevent Googlebot from ever seeing the robots <meta> tag. An indexed page that is blocked via robots.txt will likely fall out of the index over time, but it can take a good while since Google tends to retain pages. And as long as the page remains indexed, it will flow PageRank. So, if your goal is to block the flow of PageRank etc., it would be best to use the robots <meta> tag and NOT block the pages with robots.txt.

rainborick covers it pretty well. Don't forget that Google recently admitted they will still crawl a page that has a +1 button even if you block it with robots.txt.

There are also some other options you can do.

#1 - Use htaccess to block all traffic from Googlebot
#2 - Use htaccess to redirect the referrals from backlinks elsewhere.

As goodroi said, redirecting Googlebot traffic is also an option. This is the way you can do it with Apache and .htaccess:

RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} ^.*Googlebot
RewriteRule ^.*$ http://newsite.com/ [R=301,L]

If the entire site is disallowed in robots.txt, I don't see a reason to prefer meta redirects compared to 301 or 302 redirects. Either way Googlebot shouldn't crawl it. If Googlebot does crawl (violating robots.txt) either way it would see the redirect.

Thanks guys, I'll let you know how it turns out