I recommend one injector per runner -- injecting before the turbos can pit the blades. Sizing will have to be calculated -- links below to help -- the better the atomization the better it will run.
You'll want a progressive controller that is linked either to boost, MAF voltage, or TPS, and will have to adjust the tune to account for the complex mixture of air, water, alcohol, and petrol.
You'll want good check valves and a failsafe to either pull timing or alert you if there's a clog or you run out.
You'll also want to experiment with a good mixture -- pure water is best for anti det; a mixture is best to avoid freezing (if you live in cold climate) and to compensate for the displacement of fuel and air. Water must be distilled. Also, methanol and other alcohols have a lower stochiometric value, and produce more torque than petrol. Still, the ideal mixture will take a bit of playing around with. Another benefit is that with any mixture, it will cool the charge -- but also displace air and fuel, so its a balance.
You can run 95% isopropyl alcohol in the mix (cheaper, easier to get, and less toxic than methanol), but methanol tends to be the preferred alcohol. Be careful with it -- very bad stuff to get on you.
It's WWII fighter plane tech... You can find lots more general and technical info here
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On my old SC'd Celica GT-S, I ran an IM port coolingmist kit and was very happy with it.
Water Injection, Methanol Injection, Alcohol Injection Systems | water injection Coolingmist
The aquamist kit has a more slick pump, but a standard pump works perfectly fine.
All that said -- you could just tune for 93 AKI and call it a day, but you should be able to make more power and torque with water-alky injection.