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Could you consider a version of option 4? Main deal page could feature the top 3-5 deals of each of your most popular subcategories.  Then your category pages feature all the deals for that category so it doesn't seem like there would be a duplicate content issue with this approach.  This also seems to be a user-centric approach b/c it allows people to see a variety of deals on the main page and they are being curated by popularity of category and top 3-5 best sellers within the category. Does that make sense?

If you've already cut internal links and they're only in RSS, I probably would NOINDEX them, personally. You're basically telling Google that they're low-value (for now, at least) but then you're letting them be [possibly] indexed and potentially diluting the rest of your index (and ranking power). That way, people can still access them, but you're not risking Panda issues or other problems. Over time, as you add content and boost your domain authority and link profile, you can start phasing in more pages.

Don't forget the Pininterest - if you have good images, incredible SEO potential there. Also, find relevant websites who might find your images interesting - not difficult if your pics are unique and not-so-common. You can allow them to use it if they link to you.

Syndication tag can be used if you are not worried about your pages in Google news. You may also use "noindex" or "canonical" if you want to play a very safe game. But as you know, your pages won't be indexed. If you mention the content source at prominent places, you will be O.K. Example: In title you may say as "....event by ........." In the body, you may say as "...thanks to .........." As long as the overall percentage of duplicate content in your site is in very reasonable level and you link back to content source, you won't find any problem. Google clarified that content duplication alone will not lead to negative impact. http://googlewebmastercentral.blogspot.com/2008/06/duplicate-content-due-to-scrapers.html

I recently wrote to Disqus to ask how I could make comments on my site indexable.  There is an API that you can use and you can set up a mysql database to store comments on your site.  However, it's not straightforward.  I want to figure it out, but for now I'm waiting for someone else to do the work for me.   However, if you have Disqus on a Wordpress blog then the comments are stored in your database and they are part of your site and as such are indexable and searchable. I would disagree with the statement that comments are not helpful for SEO purposes.  I get a number of searches that were delivered to my site because of content in the comments section.