The first (and hardest) point is actually choosing a suitable gauge that YOU like.
My own criteria were a good quality gauge that was reliable , accurate and suited the coupe dash.
My choice changed more often than the weather.
Possible makes are Equus,TIM,Blitz,Durite etc
The two main contenders were 1 x Greddy gauge OR 2 x Autometer Carbon style 52mm gauges (Boost + AirFuel).
In the end I chose the Greddy purely because I liked the 'look' of the Greddy better............
The two types of gauges available are MECHANICAL or ELECTRICAL
Mechanical will involve you running a tube from the engine bay directly up to the back of your guage.
Electrical use a seperate boost sensor located in the engine bay , therefore you run electrical wires from engine bay to gauge
I found it easier to route wires rather than a tube! But remember an electrical setup has more to go wrong ...