I had an Autometer tach installed a few months back. Pretty simple to do, per the instructions given. 4 wires (red, black, white, and green) --- green went to the coil wire. What sorta info do you need? BTW, that tach is for sale. If interested let me know (hehe, shameless sale!).
Where & how you mount the thing is up to you (personally I prefer gauges visible to the driver while inconpsicuous to anybody else), but you ought to get a decent enough tach that has clear instructions. You can also download generic instructions off the web; just be careful in applying those.
But as far as your signal lead, you're better off connecting it to the tachometer output from the ECU--as opposed to running a wire all the way into the engine compartment for a hot source like your coil or ignition; you want to avoid that if you can.And if you get a good tach, you can.
Simpler & less risky is always better.
Even cars without tachometers have a tach output at the ECU. You can locate this lead in a Haynes manual (acceptable, for around 12 bucks) or the specific Nissan shop manual (much better, for 50 bucks). Alternatively, you might be able to talk a sympathetic parts guy at a Nissan counter into telling you which output to use. But you need to be careful connecting anything to your ECU; that is your engine's brain. Nothing fast or clumsy, no jumpers that might work loose, nothing that might ground out. Easy does it.
I put in a cheap ass 2" tach because I didn't want a big one. E-mail me if you want info on how to hook the backlight for it up to your dimmer switch and I can tell you which ECU wire to tap into, that way you don't have to run your wire all the way out to the coil, or spend an hour ohming out wires on the ECU harness to find the right one. It's held in with doublesided mounting tape and tips over when it's hot, but hey, I just wanted to know my rpms and didn't want to do anything permanent.