Since only your email subscribers have been migrated, I recommend you make one last post on your WordPress.com site, inviting people to subscribe by email over at your new self-hosted site.
Does subscribing to the redirect service keep me in the wordpress.com freshly posted / reader?
No, since you will be publishing your content on your self-hosted blog and not your WordPress.com blog, it won't appear in the Reader Topics, which only includes the content published on WordPress.com.
Can I update the posts on my wordpress.com blog from my self hosted installation?
The login for your self-hosted site will always be separate from the one at WordPress.com as they are running off completely separate databases. If you will be using a Site Redirect, you will need to update and publish content via your (self-hosted) WordPress dashboard. For previously published posts, it would make sense for you to move them over to the new location. This guide will step you through the process of moving your blog to a WordPress.org instance: http://en.support.wordpress.com/moving-a-blog/#moving-to-wordpress-org
Will I get the follow button?
I recommend the Jetpack plugin that adds many cool features of WordPress.com to your self-hosted WordPress blog, for example, email subscriptions. There are also plugins available that add a Follow button to your blog.
Are there recommended actions to take with Google?
Something to keep in mind is that the Site Redirect upgrade will not work for URLs that do not have the same permalink structure as your posts on WordPress.com, so please check those and keep the same structure for best results. As for Google visibility, this is up to Google and not WordPress.com. You have better understanding and control over how your site appears in search results, you might want to verify your site with Google.