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You can use it. Google supports cross domain rel="canonical" link element.

You can check out the Google official blog for this - http://googlewebmastercentral.blogspot.in/2009/12/handling-legitimate-cross-domain.html.

Google content guidelines say "There are situations where it's not easily possible to set up redirects. This could be the case when you need to migrate to a new domain name using a web server that cannot create server-side redirects. In this case, you can use the rel="canonical" link element to specify the exact URL of the domain preferred for indexing. While the rel="canonical" link element is seen as a hint and not an absolute directive, we do try to follow it where possible."

So you can use it without any harm to your site.

There are many ways to do it - I recommend you to read http://en.wikipedia.org/wiki/URL_redirection#Techniques

Out of the given methods Apache mod rewrite is best as it gives proper information to search engines that the page is permanently redirected. Apart from this you can use 'noindex' on old URL so that search engines do not index it.

1. It has to be a personal profile and not company profile. In case there are more than one authors to an article / blog, rich snippet implementation should be handling the same properly.

2. Right now Google+ seems to be the only way to it.

You can refer to Google's guide on author information here - http://support.google.com/webmasters/bin/answer.py?hl=en&answer=1408986.

It is perfectly normal to redirect URLs automatically. You just need to keep basics of SEO in account. Danny Dover, in his book SEO Secrets, wrote "A pyramid structure for a website allows the most possible link juice to get to all the website’s pages with the fewest number of links."

One issue which generally comes is that the old pages are properly redirected making 2 pages available to search engines, thus eroding value or URLs.

Check schema.org/product to understand how you should do it. Also Google has new guidelines and you can find them here.

**Note: **

When you add rich snippets, it is JUST HELPING search engines understand what type of data your site has but this may not help your site/url rank on search engine as the ranking on a page does not depend on it. However for right context the URL may get benefit as it is having more structured information.

So you should do it but it will work only if competitors have unstructured information