Yes, getting bigger pecs will give the illusion of bigger breasts and is IMHO much sexier than a pair of plastic boobs.
I would urge you to build up your whole body and not just one specific part though, since symmetry always looks better (my girlfriend always complains about those guys in the...
Generally speaking, light weights, many reps = leaner muscles, better endurance (think cross country skiing) while heavy weights, fewer reps = bigger, stronger (as in explosive) muscles.
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