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The key to these type of projects of the quality of the traffic, your question involved several fields but as I see just one simple goal which is to make your site profitable. Keep in mind that the key on every PPC campaign is segmentation, not all the traffic is useful and not all the keywords are useful so the first thing to check is your PPC campaign and most important your funnels GTmetrix score is not relevant in other to make sales, Google Suggest to optimize the user experience and that is an SEO requirement in order to rank a website/page (in your case I should focus on your conversions rather than performance) I will strongly suggest you add  a **cart abandon Opt-in **please check the article it will give some interesting ideas Also, I will strongly suggest you integrate a Popup in your website to collect emails and of course create an email campaign check this example https://www.jomashop.com/ A retargeting campaign will be also useful I hope these advice help you Regards