It is more common to put 私は for the beginning of the sentence. ⇒私は将来～ (By the way, is my preposition 'for' correct in this context?↑) Also, there is no need to translate "I must become (one of them)" This choice makes it more Japanese-like expression. ⇒私は将来、グラフィックデザイナーかイラストレーターになりたいと思っています。