Write as much copy as you need to convey the information that is needed for your visitor on that page.  If you can create a good user experience on one page with 100 words (by answering the pain that they would be going to that page to solve) and then you need 1,000 words for your next page, then do that to.  Don't make arbitrary copy limits or goals based on SEO, make your pages user friendly and your copy useful and your pages will rank well for the appropriate content.

Also, your Google traffic and your Adwords will never line up perfectly due to the difference of how each is tracked.

Google has gone into the differences here:  https://support.google.com/analytics/answer/1034383?hl=en

It is best practice to use nofollow tags and your robots.txt to keep search engines out of not only e-commerce pages, but also any areas that require a log in (such as a customer profile page or shopping history).  You want to do this so that they do not accidentally index pages that will redirect users who aren't logged in or create a weird/negative experience for them.

Meta descriptions do not effect your page optimization in the sense that a search engine is effected by it, but it will effect how often people click to your site as the meta description is the copy a person is shown. You should make your descriptions informative and truthful so that it accurately portrays what each page has to offer giving a potential visitor the best ability to judge what content will be on the page (and thereby lowering bounces/re-searches). This being said you should write custom meta descriptions, not just let it truncate content already on your page.  I would start with products that are relevant to the most used keywords and work backwards, if you dedicate yourself to doing at least 20 descriptions a week you will have all of your legacy products done in a year.

The easiest way to do this is to export the data and work with it outside of Google Analytics. I reccomend using http://www.nextanalytics.com/ to automatically export data from GA into excel.

If you switched from http: to https: you need to change your GWMT. Your GA account is linked to your old GWMT for non-secure, you will need to set up a new GWMT account for secure (https:) and then link that with your GA account.

Have you tried searching the account number to see what other websites (if any) are using that account? If you client's UA number does not end in a -1 then there is a good chance whomever made the site used the same account for all of the work they did, including their own site.