My room size is 113" x 124"

I have a M-Audio audiophile 2496 sound card

I do not have monitors as of yet. (Please tell me what I should get)

I am thinking of making the insulation bass traps for all corners in the room. Is this wise?

Before now I have been mixing on my pc speakers. (Sounds lousy on any other system) So I switched to headphones. I have been using Sony MDR-XD200. They are better than the PC speakers but still are not doing the trick.

Any help I would greatly appreciate.
Thanks