These are my main four and the reasoning behind it.
Boost- potential leak or over boosting
AIT's- heat soak anyone?
Wideband- not only does it tell my tune but also condition of my spark.
EGT- not for tuning only, potential spoter of a bad tank of gas.

 

if you're going to use the center dash speaker place for triple gauge pod, you can have the PFC commander right under it with velcro, so everytime you check out your tri gauge pod, you can also easily see the PFC as well. and since pfc can display water temp and boost, and also record the highest readings, i would just use PFC to view boost and water temp, have the tri gauge read oil temp, oil pressure, wideband, and the steering column, oh, i wouldn't need one on my steering wheel :P

 

I don't think the aftermarket oil pressure gauge is too crucial, the stock one can be kinda finicky but oil problems aren't usually an issue in the RX7.

Oil temp could be helpful on a track car, unless you have enough oil cooler capacity that the oil temp is never an issue.

I like being able to see my afr's and my fuel pressure. While on a properly running car they may not be necessary, when you do have a problem it's nice to have to help diagnose things. Then you have a basis of what your car normally runs at, and any changes can be noticed early.

A boost gauge is definitely needed, boost issues are very common on turbo cars and keeping an eye on that is important for the health of the engine as well as power output. I usually find myself looking at the profec b more then the boost gauge though.

EGT's are nice to have as well, but on a lower HP car (350HP) probably not a crucial instrument.

I use the PFC commander for water temp it works quite well.

 

First thing is to make all the stock gauges work as they should...

Water temp can be monitored with the stock gauge if you add the "linearization" mod to the circuit. I assume that this mod is archived on the forum. If not let me know an I can re-post its from my archive.

Oil pressure requires the periodic replacement of the Mazda sender... I still don't understand why these fail as often as they do.

My next choices in order of how often I refer to them...
1) Boost - mounted on steering column for quick reference
2) Oil temp - I have an aftermarket system and the thermostat is the weak link.
3) Fuel Pressure - I have lost one engine due to a bad fuel pump
4) Volts - I monitor this with the PFC commander. I fried a battery, an HKS twin power, the air bag CPU and the ABS CPU from a failed to over-voltage alternator

IMHO - AFR and EGT are best data logged to a PC. I don't think that a quick glance at a gauge can tell you much realtive to these measurements.