Nope, won't cause any problems. The xml sitemap is what you will submit to G and search engines while the HTML one is for your site visitors who want to see all your pages (although it will be crawled and indexed as well).

Try this. It uses the web.config file which is accessible via FTP.

Move charset="UTF-8"> immediately after the opening

If you plan on translating a part to another language, I would use the hreflang tag to tell search engines that two pages are identical, just in different languages. Then search engines can serve the correct version of the page to whoever is searching based on their language preferences.

If a nice chunk of your customers prefer English, I would look into creating a English version of your entire website.

You should utilize og:locale:alternative and have og:locale set to the country you want to present it to. see details here.

Overall, since its English in both scenarios, I don't think you need to worry about it.