Clifford Matrix RS2 on 01 Echo

I have installed many remote starter and keyless entry systems, but this will be my first time installing a full alarm system. It is the Clifford Matrix model RS2 going into a 2001 Toyota Echo. From reading through the install guide I have come up with a few questions.

What is the function of the dome light supervision circuit? My guess is that it turns on the dome light when the alarm is disarmed and the doors unlock. Is this correct, and do most customers want this?

Is there a recommended place for installing the siren?

Is there a recommended place to install the dual stage shock sensor?

In the box there was a mercury switch, I don't see a reference to that in the install guide. Where does that go?

I'm also reading that there may be a problem with ignition isolation. How common is this problem? I also have seen two methods for correction, one breaks the ignition wire the other breaks the starter wire. They both appear to work, but is one recommended over the other?

The car doesn't have a factory alarm, keyless entry, or power windows but does have one main switch on the console for power lock and unlock of all doors. I assume I can tap into that circuitry to use the keyless entry feature of the alarm system. Is this correct?

Lastly, the tach vs voltage sensing mode. In all the remote starter installs I have performed, I always use the voltage sensing mode and haven't had a problem yet. These were other brands like Crimestopper and DesignTech and they included the tach option, but the voltage sensing was the default. This DEI model has the default as the tach. Do, I really need the tach wire?

That's all I've come up with, if anyone else knows of something important, or just a helpful tip I would like to know.  Thanks.

Dave

One more thing. Whats in document #1041 Door Lock Wiring Guide? Since I'm not a DEI dealer I don't have access to it.

I hate these places that want you to pay for everything, most other manufacturers provide that stuff for free.