Hi.
From my(and few others) experience body weight isn't much of a deal.
You can start with 10-15mg and up the dosage when you fill comfortable. Correctly vaped ~30mg should be enough to "knock down" most of the people.
You may find absolutely insane people on youtube vaping 50-100mg spice for no good reason with absolutely terrible vaping devices and technique, and calling their crazy dosage and crappy devices(e.g. plastic bottle + tin foil) best methods for breakthrough. Forget about them.
No idea about your vaporizer.