Those 2 gauges are the gauges that I was going to suggest : EGT and Oil Pressure Gauge. EGT is important because you have a NOx setup. Oil pressure is always good to have just in case oil pump fails or there is a big oil leak that you don't know about. Instead of oil pressure, maybe oil temp, or even vacuum/boost gauge.
I have oil pres., A/F, and voltimeter on my car along with SAFC which shows engine vacuum because I have a MAP sensor.