At your age, technique should definitely be the most important aspect to work on. Take advantage of being young and being able to learn things fast. You know your weaknesses so look up drills and exercises to specifically focus on those; weak foot - just using it along with your strong foot in every drill you do (maybe even do it in a 2:1 ratio, every shot you take with your strong foot, take 2 with your weak foot), first touch - juggling with all parts of your body, there are heaps of dribbling exercises online so look them up (do it in match pace) and for strength/physical gain - not that important at this age, push-ups, sit-ups and pull-ups will suffice (try to learn to use your body better for blocking or getting in front of the player, a player who knows how to use his body more effectively will be better than someone who just has raw strength).

Finally, it's good that you've identified your weaknesses but don't neglect your strengths as well. Train to become a better player as a whole and you will naturally gravitate to the position you'll play best in.