I was going to suggest getting 3 cases at a time, which for my toy room is nearly floor to ceiling in height. I wasnt sure what yout budget and space were like though.
I'm going to save you a lot of trouble here, the assembly instructions for moducases are a QR code to a youtube video which is their old design, (holes are already made for the light screws, the rubber strips are already on the side panels, that isnt true anymore) so dont even bother warching it, just watch other videos of people assembling them.
put them together on a table that you dont care if its scratched, and lastly put them together at the same time. Its a lot easier to build 3 together than 3 separately.
My least favorite part of them is the lights that come standard, they are more spotlights than anything, so plan on getting some nice LEDs instead. Otherwise it will be very dark.