I got a Blitz r-vit TypeII in my r32 skyline.
It plugs into the consult port near the fuses.
It only shows ECU details.
Doesnt have any external sensors, only reads ecu information. (no different to plugging a laptop with consult cable)
Displays all sensors which the ecu reads;
water temp, afm voltage, o2 voltage, injector duty cycle, ignition timing, battery voltage, speed, rpm
In regards to question 4, you are after a single unit which can display external sensors for water temp, oil press, boost press etc.
Only option ive found on the internet is Defi Link - http://www.nengun.com/defi/link-display
Although after buying all the sensors etc, it will set you back close to $1k