start small.when cutting coils i usually cut 1/2 wrap at a time> reassemble suspension. lower vehicle> bounce it a few times> measure clearances> maybe test drive> stand back and eyeball vehicle's stance> repeat.
once you have cut off too much there is no rebuilding a spring. do not use a torch to cut. hacksaws are the safest maner. metal cutting blades aren/t too bad imo as long as you don't try to cut all the way through in one try and monitor the heat of the the spring(i never let them get hotter than i can touch with my bare hands).