The first thing to as is where do you think you're going to be reading the info that the gauges provide?

Because if you're thinking "everything will get shown on the plotters" you may want to re-think that.  It *really* helps to keep important info like engine RPMs, oil pressure and temperatures out and visible on a separate display.  You *never* want to be in a situation where that data isn't constantly visible in front of when you're running the boat.  Small changes in temp or pressures are THE early warning signs that something is amiss and should be dealt with RIGHT NOW.

Using a chart plotter for this looks fancy in marketing literature but in real life... it's often not ideal.  I know, I've tried and keep coming back to using dedicated displays for the engine data.  

So take a hard look at what fits on your console and choose wisely.

What you use for the display will have /some/ influence on the way you'll get the data off the engines and onto them.  There are a whole range of sensors-to-NMEA2000 options out there.  Bearing in mind you need sensors for a whole slew of things.  Oil pressure, water temperature, RPMs are the basics... then there's exhaust temps, engine load (if you have diesels), transmission pressure/temp, etc.  Depending on the engines some of that might already be available via J1939 interfaces to them.