Q:

How vigorously should I heat my moka?

I usually use a moka pot on my gas stove, and on the smallest flame adjusted so it's roughly the same size as the base, I get good results.
However, when I'm at my parents', I use their moka on an induction hob, which is very fierce. On the hottest setting, the moka practically explodes - boiling over (even from cold) in a few seconds with a powerful spurt of superheated steam - not ideal.
My question then is how do I judge what setting on the induction hob to use for a good brew? How long should I expect a 6-cup pot to take to start extraction? Is turning down the heat once extraction has started to prevent the violent spurt at the end a good idea?

A:

I'm going to start by answering your last question first just for fun. In this site, it says that:

Place the pot over a low flame. A low flame increases the brew time, which enhances the flavor. At a later step, you’ll want a slow trickle of espresso instead of a full-force fountain.

You would want a nice, long brew time. The flavor will be enhanced rather than the quick brew time with a large fire. So flavor and brew time can be changed depending on the size of your heat. To answer that question, YES it is a great idea to turn down the heat. EXTRA: The site also shows how to make a nice moka (not spam)! Second, you really answered your last question yourself. Low heat is better than high heat.
Now I'm going to answer your second question. Looks like this site uses Italian pots just like your induction hob. For stovetop pots and not stovepot pots, it says that:

When the water in the tank has been exhausted, that's when you hear the ‘gurgle’ that signifies the drink is ready to pour (approximately 4 to 5 minutes).

Looks like 4 to 5 minutes is just the right time for the coffee to be ready for extraction here. You should know the sound of someone using mouthwash and gurgling. The coffee pot will start to produce that sound when coffee is ready.
Now I will answer your first question. I can't seem to find any significant information on your question, so I'll take a shot at it. 

Supposedly, it might be your decision. 

Maybe some people like this setting while others like another. I don't know what your standards for a good brew is so I'll just say that you should choose it. Sorry for the lack of information! I hope this answer answered all your questions!

