As a lefty who is proficient with the numpad, I’d adapt quickly to it being on the left, but I wouldn’t ultimately be any faster with it, regardless of whether key order was reversed or kept the same.
I also don’t think I’ve ever seen a lefty who prefers (or at least regularly uses) a left mouse. I adjusted to right for the same reason as you, but I also think being able to type one handed with my left while mousing with my right is superior to its opposite for me.
I would generally type with both hands at the same time, but it is useful to be able to mouse with my right hand and do the common shortcuts (ctrl+z,x,c,v) with my left. I don't know how that would work if I was mousing with my left hand. I'd have to control with my index finger and do the shortcut with my little finger? sounds awful lol