generally cutting the coil springs is not the best solution to lowering a car. if you do cut them, the perferred method is a cut-off wheel not a torch.
The best solution to lowering a car is new springs with a lower spring rate, such as a 6 cylinder spring. When you cut the springs, the rate of pounds/per inch stays the same and the suspension stiffens (ruff riding).
But, if you cut them, cut the end that isn't flattened and start with 1/2 to 3/4 coil. Yes, it is a lot of work to take it out a number of times, but you can cut too much the first time by guessing and cutting a coil or more.