We're upgrading from 7 to 13, which is a rebuild. Are there any known SEO issues I should be aware of, as in will my organic SEO be impacted? Thanks

With some of our clients, we've experienced a very brief hiccup as Google recognizes some changes and has to re-crawl. But if you structure your site similarly to the old one, ensure you include any meta tags, necessary content, etc... it should rebound quickly. You may not even see a drop, but in other cases it can take a few months to recover. Overall, we've seen major improvement in visibility with newer umbraco versions. 100% recommend.

Can I add a warning on non "standard" characters. E.g. accented characters and arabic. Found that one site changed the urls so make sure you check for this if you have these in your URLs.