If you want a system that sprays based on boost then an Aquamist kit may not be for you. Aquamist kits spray primarily on injector duty cycle.

The only way to reduce boost and timing is to use the test connector on the car. I know this works for the earlier generation STI's, I don't have any feedback on your model as of yet.

The Aquamist kits utilizing a gauge have a low level sensor indicator on the gauge.

There are many places to buy tanks. We can supply you with many options. 3 gallons will be large int eh back of the GR unless you use the spare tire well.

Pre-turbo changes the profile of the turbo compressor map, otherwise you can put one or two injectors after the IC. There is no guarantee that pre-turbo injection will not affect the compressor wheel, but there are a few methods to minimize the affects.