I am looking at some gauges online to purchase for my car. Mostly looking at the Lunar 52mm series from Autometer. I just need help picking up 3 more gauges. If you guys could help me out with some simple questions for you probably but unknowns for me. Thanks!

Water Temperature Gauge 100-250F [electric]
1.) Where in the engine does this go/excatly what water temp does it measure?
2.) Is it really one of the more important ones to have?

Pyrometer 0-1600F [electric]
1.) Where does this one go?
2.) What would it be used for?
3.) How important is it?
4.) Why does the temperature go up so high?

Trans Temperature 100-250F [electric]
1.) Does this measure the transmition fluid temp?
2.) What does it do for a stickshift?
3.) Is it one of the more important ones?

Boost 35 PSI [mechanical]
1.) I want to wire this up just for the Nitrous boost, is this a good gauge to do it with?
2.) How would I connect it to see my boost from nitrous when I am on the button?

I am also getting/have goten these gauges already:
Oil Press. 2 1/16 [electrical]
Volt Meter 2 1/16 [electrical]
Fuel Pressure 0-100 PSI [electrical]
Air Fuel Ratio [electrical]
Nitrous Pressure 2 1/16 [mechanical]

1.) Out of the 4 listed which 3 do you guys think that I should get?
2.) I heard that since the Nitrous pressure gauge is mechanical, having it inside the car might cause problems and might break? Is this true? Any input? I want it on the insdie what can I do?

Thanks guys!

Any additional input or information about the gauges or anything let me know please.