I ordinarily shoot about 40# for target, 50# for hunting. When learning to shoot LH, I had the luxury of starting with a 25# LH bow that I use in my classes. It really allowed me to hone in my form LH without struggling. I am comfortable now pulling 35# LH, and okay with 40#. Probably if I shot LH more often, those comfort levels would increase.
For me, a right eye dominant person, the greatest challenge shooting LH was aiming. I see two arrows when I aim LH, and have to decide which one to use. After shooting a few shots, I remember, but it is likely in a pinch that I would misaim. BTW, if I DON'T see two arrows, that means that I am focusing on the arrow tip and not the target, and the vision of the arrows has converged, so that has become a clue I pick up on and can correct in advance of the shot.