That is true; the keyboard tray is only 2' wide. However, my daughter uses a Logitech trackball mouse which remains in place, and it works perfectly for this type of desk setup.

There is 2 1/2 inches from the bottom of the desk to the top of the tray.

Can't give exact size but it did fit in the back seat of my Toyota Camry on the floor. So it was about 36" high and 55" long and about 6" wide.

I am not a handyman kinda guy. It took me quite long time to figure out the assembly (around 2 hours and I was doing it myself, no help from anybody else). But if you have somebody to help, especially during fixing those screws to the glass from the frame (It's really difficult part as per my POV), it will take you one hour.

39.5 inches by 23.5 inches