The only way to tell if your system pressure is below zero lbs, would be to view the low side gauge. It has two scales, Pressure and vacuum.
Buying a meter to gauge how deep of a vacuum you have achieved, is several hundred dollars. A micron tool is probably over kill on automotive work. Millions of repairs and recharging have been done with the gauges in your kit.
When you get to the point of evacuation, your going to be like the majority of people who see the low side gauge is pegged out at 30", and run the vacuum pump 30 more minutes, just to be safe. This is false thinking, but very normal.
Hats off to you for atleast investing in a vacuum pump. Feel free to contact me if you have questions.