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Moz Pro Local if you are worried about duplicate listing for your business I think is the best solution. This is just my opinion there are other useful tools but I don't have experience working with them. Maybe you should give it a try Whitespark Local Citation Finder SEOProfiler SEOPressor

Can you personalise the content to each location? For example list UK customer case studies on the UK site. This will provide a more personalised experience for the user, and may also reduce the risk duplicate content. If the identical content does not need to be personalised (like the terms and conditions page for example), then you could just rel=canonical the identical pages 1 one page. thanks

Like you said, you're going to want to redirect all http versions to https. And then redirect all www. to non-www – which you can usually accomplish by setting your non-www as the primary domain. Depending on where your site is hosted / domains are registered, there will be a few different ways you might go about this. My agency uses WPEngine to host all of our sites, and they make it super easy. Regardless where my site is hosted / who my registrar is, I've always had a lot of luck chatting with their support team. For more specific redirects, we utilize the Redirection plugin. Is that helpful at all?