intersection of twisted boxes and gradual change

Hi,

i have a couple question.

as in the image i would like to make a series of box twisted along a curve. but have 1 problem and 1 more wish than my own done.

firstly, i don't want to see seperation or intersection of boxes while opening and closing curves. so that i tried to use 'solid union' to make a whole surface but couldn't be succesful as far.

secondly, i would like to change the scale where boxes rotate in order to control emptiness gradually that created by an arc at the bottom. i also tried to divide curve by domain and apply 'scale' factor in it. but it didn't give the desired effect..

the file is attached

Thank you thank you!