> 1. Does the inside of the closet need to be treated? <
Not if the door is rigid enough to reflect bass waves. Is the sliding door regular wood? If so, it will reflect bass so there's little value in treating inside the closet.
> 2. Does window need to be treated or will blinds reduce the bouncing back and forth? <
It depends on where you and the speakers are in relation to the window. If it's not at a first reflection point I wouldn't worry so much.
> 3. My corners either have some obstruction (door, closet, furniture) where do I put bass traps? <
In the wall-ceiling corners. Or set them on the floor leaning against the wall.
> 4. I only have three walls to chose from to place my 2 near field DAW and subwoofer. Where should I put it? <
You're hosed.
Seriously, the top wall is probably best, as long as you don't mind partially blocking the closet.
> 5. Does sub need to be symmetrically centered? <
No.
--Ethan