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are you looking for design galleries to submit your web design to, or are you looking for news sites that will talk about your web design in a news format?

Normally i would go with a url that is less then 20 characters as most people can remember 20 characters or less.  The recommended of what I have seen is 3 to 40 characters.  But Google, from what I have seen does not tell you what they recommend.  But remember, Google looks for a good user experience and a shorter url promotes people remembering your site, which in turn is a good url experience,

it could be that your tags and categories are considered individual pages and therefore creating their own permalink: ex: http:www.example.com/keyword, and http://www.example.com/tag/keyword and http://www.example.com/category/keyword.  Another way would be to check the sitemaps you have in webmaster tools and compare those to each other.  Just a suggestion.

Yes your keywords are certainly related to one another, but each deserve their own post.  So why not pick your primary keyword and two secondary target keywords and put them in the post.  Then use your secondary keywords as links to your other posts about those keywords.  Increase the amount of juice, cover your bases, and be relevant.  Just a suggestion.

Have you considered consolidating the pages? What I mean by that, is if each product has its own wp post then how about sorting it by color, so yellow shirt and blue shirt don't have separate post but one posts with a variation tool within to delineate the colors. Then 301 redirect those old permalinks to the new one?  Also, it might be time for a migration like irving weiss said, in which case I would recommend Magento as your eCommerce platform.

If I understand you correctly about ranking delay, you mean can you shoot up directly as soon as you start trying to rank for that keyword? If that is the question, here is my answer.  You can rank for a highly competitive keyword if your content is relevant and you have enough clout (pr rank, backlinks, authority).  Otherwise it will take a while to establish yourself as relevant.

I agree with Andrea that the SEO moz tool is good to use to determine competitiveness of the keyword, there is also google adwords like Andrea also mentioned.

I use constant contact and occasionally mail chimp.  Constant contact, in my experience, is the most complete.  It gives you analytics and all the data you could possibly want.  In addition it gives you video tutorials on how to use constant contact and what you get in return, as well as click throughs and things like that.

If you want to do it yourself however, what you do is set up conversion codes within your google analytics or whatever analytics tool you are using that redirects to the specific page within your site and track the click throughs that way as it will appear as part of your conversion code in your analytics.  I don't have much experience with this method as I prefer to use constant contact because of all the functionality that it provides.  I hope this helps with your answer.