The best is to choose a mobile friendly theme. Make sure it pass Google mobile-friendly test: https://www.google.com/webmasters/tools/mobile-friendly/
Most themes are mobile friendly unless you are using a really old theme.
For the 2nd part, please refer to your question earlier. http://www.askimpossible.com/plugins/issues-with-mobile-friendly/
Thanks for the tip! I have decided to change the theme altogether because that theme though indicated as mobile-friendly does not look good on mobile phones when re-ordered.