It depends on your Barley box size. My squirrel cage has three speeds and I like the 1100 best. 1000 should be fine but be sure to check out the decibels. Read some threads here on that subject and how peeps have dealt with it. I made a four foot one and found I was hating full length rods. I cut my rods in half and it was much better. I reread your post and see the decibels are 39. Not bad.
Good luck. As with all studios we are always tweaking them, they are in a constant state of flow and ebb. Took me three years to get the chair, arm rests and seating PERFECT! With that small of ducting make sure you install smooth ducting.
Have fun and remember the chocolate or whatever your go to food/drink is.