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If you click on "Admin" in the top right, then under "View" click on "Scheduled Emails" you will see the scheduled emails for that profile. On the far right you will see "Actions". Under the actions button is the option to delete.

Yeah, I would 301 redirect all of the old blog articles to the new blog articles.

The big difference, as far as SEO is concerned, for a subdomain blog (blog.) versus a directory (/blog) is how the link credit is attributed. Search engines see a subdomain as a completely separate site. Any backlinks you get to your blog content will only benefit your subdomain blog. When the blog is a directory it is an extension of your main domain. When you have it set up that way and build content the backlinks received for the content can help build the domain authority. I personally prefer to setup blogs as /blog and would recommend that method although I have also seen people successfully have subdomain blog setups as well.

I would definitely avoid leaving a bunch of URLs as 404s. Even though it would be time consuming I would really try to 301 redirect all of the old pages to the most relevant current page. That would definitely be the best long term move. If you really can't do that you can 301 redirect all of the old forum pages to the new forum. Instead of redirecting to the most relevant post you can put them to the beginning directory of the new forum so at least they aren't receiving a 404 and can hopefully search for their issue there. If you do leave thousands of URLs with 404 errors I would continuously check Google and Bing Webmaster Tools for crawl errors. The webmaster tools will identify URLs they have crawled and found issues with and at that time I would just start fixing them one by one and redirecting to the most relevant URL. That way, over time, the URLs will eventually be corrected. Hope this helps.

I actually show both terms graded as a C for that page. If you run the page grader again (http://pro.moz.com/tools/on-page-keyword-optimization/new) it actually lists out exactly what items it looks for and doesn't find and those are the reasons why the grade would be lower. If there is a green check mark to the left of the item then that means it was able to find this on your page, if the green check is missing then that is something you should focus on.

Adwords considers a conversion to be anyone who clicked on the ad and then converted anytime within 30 days of that click. Google Analytics associates a cpc conversion if it was the last action taken prior to converting, so if they clicked on the ad earlier in the conversion process it doesn't count it. You can look at the multi-channel funnels reports to try and get a clearer picture of how AdWords is effecting conversions.