In terms of gaining 'powerful strokes' you are much better served refining your swing rather than building strength in a gym. I'll also say that regarding injury prevention, having good fundamental strokes and movement is also just as (if not more) important than building strength.
regarding the 'things you heard' regarding weight training, the basic understanding is this:
low reps (1-6)= strength training
medium reps (6-15)= hypertrophy (ie. muscles getting bigger)
high rep (>15)= endurance
basically there's nothing wrong w/ lifting heavy. you will get stronger. This is esp pertinent in the lower body... as you gain lower body strength you will be quicker and more explosive.