Good question. I have been thinking about that too as I am getting close to that point.
For the trim, I had planned on attaching 1" furring strips to the wall and then attaching the trim to that. The reason for the 1" furring strips is because my fabric panels will also be 1" thick. In my case, the lowest channel on the wall is 2-3" above the floor level, so I should be able to attach the furring strips to that. Will probably rip 1/2" ply and double it up to make the furring strips (as well as the fabric frames). Very much open to other suggestions though.
For the columns, I attached 2x2s to the walls using construction adhesive and screws into the channel. Once I have the columns wrapped, I will attach them to the 2x2s with finish nails.
I plan to just friction fit the fabric frames/acoustic panels until I figure out the final treatment plan. Once I am happy with the room measurements, they will probably get the construction adhesive/finish nail treatment directly to the DW for final installation.
I'm sure there are other methods, and I would love to hear them!