I hope your room comes out well. I sure like the dimensions.
Building an optimal audio room is not a simple undertaking. Regarding your question:
- Rockwool will help isolate the room from outside sounds and vice-versa. I recommend it. There are other methods used to increase isolation, mostly various methods of wall construction. (A caution: the more successful the isolation is, the stronger the bass nodes and peaks might be.)
- Acoustic treatments (panels, bass traps) in the room will control reflection, absorption, diffusion of sounds within the room. They're how you reduce slap echo, first reflections, and bass boom.
One does not replace the other.
I suggest trying to read more about all this before finalizing your plans.
GIK and ASC will provide treatment plans for a small fee. ASC also will consult on room construction.
Have fun!