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Ok do a thing. First figure it out what type of links they are - directories, social book mark, article submission sites, RP sites .. _Once you are done, you need to sort them via PR and look at the anchor texts. If they are exact matched keywords, you need to get rid of them, do not do anything with natural anchor texts like click here, website name etc. _ _Look at the quality of the sites from where the links are coming.. check their moz rank, check the quality of the content of the website... if they score bad in all these fronts, just get them removed and you will just be fine .. _

Thats odd. If there are no such URLs they should not longer index automatically. You can go into WMT - Webmaster Tools and Optimization>Remove URLs. Also resubmit your sitemap if it doesn't get done automatically.

I'm pretty sure you don't need to worry about that for duplicate content. I've never used Shopify but believe they host the website for you. In that case I would ask them to fix this issue for you. Here is .htaccess code to remove trailing slash though: RewriteBase / RewriteRule ^(.*)/$ $1 [R,L]

Nah. Ditch em. Article directory links are pretty garbage these days. Any miniscule benefit they may still provide isnt worth the headache of wondering if those are the links keeping ya down. Also if you ever have to do a reconsideration request it'll be one less thing for you to clean up because under a manual review there isnt  google engineer out there who isnt going to frown on them links.

I noticed that on most product pages you do have lots of content repeating itself. For example - PRODUCT DETAILS, SIZE GUIDE etc. The product pages are relatively thin with content, and the repeated content (duplicated) is larger than the "new" content. Maybe you should change those to images...?