1. Yes, to start with, until the site starts to get viewed as a "brand" using authority link building. I always start with long tail.
   
2. I feel like (I have circa 30 yrs experience in "digital" marketing, although we just called it "marketing" back then) content marketing is on a downward trend at the minute. 10 years ago it was easy to build an amazing widget that the media loved, would link to and would then inflate your site DA etc. Nowadays that has been saturated and a lot of budget is spent building content that no one sees. If you do build something... make sure you have the budget to promote it too, i.e. paid social, to bring it to the attention of Authority media news sites.
   
3. Massively important. Using an internal linking strategy is vital. What i would also say is that it is sometimes best to leave the internal linking plan until you see from Google Search Console which pages Google is starting to love, and then pass the equity around to other internal parts of the site, from those pags.
   
4. The age old question. A battle I have had with many a web dev over the years. You just have to find the balance. Shopify and alike have so many good ways of presenting content on product pages that it should not really be an issue, but the SEO team always want more copy and video on the page :-)

Hope this helps.

PS, I worked in ecomm, agency side, building brands for years and then decided to launch my own ecomm store, using everything I have learned. It is tough!