I wouldn’t think a different laser is going to effect your hair removal results. In fact, going to an alexandrite laser might even be more effective. I believe GentleLASE is an alex and is a good machine, especially in the hands of a good tech.
10-12 weeks seemed (for me) to be good spacing for treatments, though sometimes I went in as early as 8. I found if I waited a little longer, there would be just a little more hair there to have treated. However, waiting too long will be counter productive because some hairs will pass the growing stage.
What I’ve read about the effectiveness between lower and upper legs to be true for me. My lower legs were much more hairier but they responded quite a bit better than upper legs with LHR and electrolysis. It is odd, though, the knees which had the least amount of hair seems to be the least responsive. But, over the course of time, between LHR and electro, there is hardly anything left except for the nearly invisible, slow-growing, very fine hair.