You do have a lot of questions. We will try to answer them with as much detail as possible.

1. Many of the kits listed, except Aquamist, are what is called Progressive Pump Speed Systems(PPS). These kits change the speed of a pump to change the amount of injection. The Aquamist systems use a constant pressure pump and a control vis a valve similar in junction to a fuel injector. The Aquamist system acts similarly to a modern fuel injection system.

The merits of PPS systems are that they are inexpensive and have few components. The drawbacks are they don't track the engine load very well and have a very poor dynamic range. This can lead to erratic AFR's over differing load ranges and difficulty in tuning for proper driveabilty and power across a broad range. There have been entire papers written on this, we can refer you to more materials if you like.

The merits of the Pulse Width Modulated Valve system (PWM-V) that Aquamist uses are precise injection across all load ranges of the engine and repeatability across the same load changes. This leads to precise AFR control maximizing efficiency and power across the whole load/rev range. This is due to the wide dynamic range of the systems.

Any system can achieve the same max power output on the dyno in a narrow rev range if jetted right, it's all other aspects of the rev range and driveability where the differences can be significant.

2. MAF or Boost are the general means of injecting for the PPS systems, a few track IDC. Aquamist uses Injector Duty Cycle(IDC) as it's primary reference for controlling the injection amount. IDC is the most effective measurement of load on an engine thus generally providing the most accurate means of injection. Some of the systems including Aquamist(some kits) allow a mix of IDC and Boost to control the injected amount.

3. Depending on the type of system and car the install time can vary greatly. The time really changes with where the jet is installed(how much of the engine/car comes apart) and how clean you make the install. I would guess time can vary anywhere from 3-8 hours. You should contact a shop that has performed installs before and ask what they have experienced in the past.

4. This really depends on the engine configuration and mapping. If you are octane limited and have heat soak issues you could see a benefit without tuning. Some cars have lost power by bolting on a kit and not tuning for it. We would need more specific info about your application to dive deeper into this.

5. Again, see above. This depends on how octane limited you are at the moment. If you have the ability to increase boost and timing with more octane then increases in TQ and power can be realized.

6. We have done this in the past with some systems we have built. These utilized a quick release tank/pump mount, a quick disconnect for the power/control wires and a high pressure quick disconnect for the pressure line after the pump. It can be done, this just depends if the benefits outweigh the costs in your application.

7. Again, see 4. This really depends on the amount of boost and timing you can add to your configuration. Some of the stock 2.0L WRX engines in the States can see quite significant gains, while other makes of cars with more limitations won't realize as much.

Let me know if this helps and we can elaborate more in more specific areas.