The only thing weight does, is more or less effect how long THC will stay in your body, since it is fat soluble, on average the more fat the longer period of time. Other factors that affect this would be your fitness level and diet.

Your first question is answered by saying, for a beginner I suggest inhaling into your mouth and allowing it to cool for a few extra seconds which is what saliva helps do, then inhaling fully into your lungs, and dont swallow. Swallowing usually throws off most newbies.