Which gauge is more important? Which temperature levels is more important to monitor for reliability, overheating? also, what is the normal levels of exhaust gas temperatures and if they get to high what are the effects?

 

they are both v ery important, if you can only get one now, get the water temp as that is the lifeblood of the rotary motor, and the stock one if horribly inaccurate.

 

The stock gauge will not rise beyond middle until you've just about toasted the engine. Poor design, by far! Get the water temp gauge first, so you'll see the any abnormal rise before it becomes a nightmare.