Given that there are many commentaries on the torah, should one spend all his time allocated for this study on understanding them or should he spend some of it deriving his own chidushim (novel insights)? Is there a different in this between the different types of torah study? (chumash, nach, talmud, hashkafa, etc.)
Even if there are "many commentaries on the Torah" as you pointed out, no one will be able to come up with the chiddushim that only you can. Chazal say that "just as no two faces are exactly alike, so too no two people have the same knowledge and experiences in life." [Brochos 58a]
That said, chidushim should be (I think) something that comes to you naturally. HaShem is speaking through you. The more you learn, daven, refine yourself, and strive to come closer to HaShem, the more you will be a conduit for novel ideas.
So, part of the answer to your question is how much are time are you already giving to learning, davening, refining yourself, and coming closer to HaShem?