new project...need some help please take a look

i am currently stripping my 91 gsx down to nothing and have some newb ?'s. what i need to know is-
how can i wire up a switch to turn the car on and off, as if i were using the key?
do i need a mechanical or electrical oil pressure gauge?
can i use the stock tach wires to hook up an aftermarket tach?
which is the best spot to tap in for a boost gauge....i had my autometer gauge tapped into a vac hose above the brake booster and it worked, but am wondering if the lines on the throttle body are better to use.

the car has already run a 10.9 @ 93 mph in the 1000ft. which puts it at an estimated 12.9 in the 1/4 with very little lightening. now the car will weigh almost nothing campared to a stock car. i can't wait to get it all done. i will post some pics soon so everyone that is interested can follow along.

Thanks guys!!!

I use electrical oil pressure gauges only.

Any manifold vacuum line is good for the boost guage, but if you want t be picky, avoid using that line for the FPR.

Not sure about the tach or the ignition switch. People hook tachs up all the time, I'm sure it uses the rpm wire to the ECU. If not, then something off the ignitor.