A very interesting project with a great start.
I agree with JB re the poles, which kind of draw attention away from the major feature, the comfy seaty boxy thingy.
Regarding the curtain, have you thought about fixing it to the roof, rather than to the outside. If the roof were removable then you could make two, one with closed and the other with open curtains, switching betweeen the two as required.
Please continue to post progress.