Marco, it sounds like you're getting the hang of the moka pot and getting some nice results from it. You are right not to tamp. One could, but only very lightly. Best is what you are doing, and tweaking brew time with grind fineness. I had forgotten you had a grinder, and assumed you were buying pre-ground. As for pre-boiling the water, I suppose it doesn't matter as long as you're not boiling the water during actual brewing itself. Re. your question on brew times, I think it varies depending on the size of your pot. The little ones will be done quicker, obviously. I recall getting good results with a 6 cup pot and a brew time of about 3 to 4 minutes or so. Remember, this isn't like a pressurized machine where you're shooting for 30 seconds.

Good to hear you're enjoying the moka pot!

Cheers,
Svend