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。