Just received my Raspad:
Seems straight-forward enough to assemble (take care to open up the slot for the ribbon cable for the micro SD card to insert it)
To install the .deb file, just download it, then open it — Carbide Motion will get installed under Graphics (which I find a bit confusing — Accessories would be a better fit?)
Before you do that though, be sure to update using
sudo apt update
sudo apt full-upgrade
&c., see:
if any adjustments are necessary.