Ok, if you're serious, you'll need some tools. SEMrush and ahrefs are basics. If you hunt around you'll get a 30 day free trial of semrush, yes you'll need to enter your cc details but just cancel once you've done your homework, it's $99 a month, I use it daily. If needed I can run some sites through it. Ahrefs have a free trial 7 days or so, again I use it daily, the cheapest package is $99.
You're using these tools to analyze the competition, content, back links, do they do paid etc. There are tools like POP (page optimizer pro) which can help with on page content and number of H tags etc. Some of this can be done manually by essentially visiting your top competitors and then looking at their H tags by going to page source and counting how many of each they have. POP does this grunt work for you.
SEMrush will give you searches per month etc for keywords, some back links that your competitors have etc. It's a must have for any seo, as is ahrefs, I don't bother with majestic doesn't cut it for me.
How many images of each item do you have on the item page, are you adding alt text and naming the images properly ?
If you search for a keyword in google and you see other words in bold, those words mean the same thing to google and you can use them within the page content to add more relevancy without overcooking the main keyword.
Primarily you want the technical and onpage up to par first before link building. Technical is the likes of relevant schema etc. Onpage is H tags, content, keyword density etc. You can use the header and footer plugin to add schema. As for page interlinking, keep it as relevant as possible, I know ecom sites have pages like recommended, other buyers who bought this also bought etc but your silo pages must be product specific.
