Your list is fairly similar to what we’ll be putting in our Rocket (although I like two coms, so we have one more…). To answer your question directly, there is no requirement for back-up engine gauges. In fact, all of our airplanes are single-string on engine instrumentation, with the exception that they all have an oil pressure switch driving a dedicated light on the panel if oil pressure drops. I’m comfortable operating a Lycoming with just an oil pressure light to get me home - I can do everything else by sound and performance.