Toto includes toilet seats with their one piece toilets, you would not need to purchase it seperately.
According to Toto the unit you would be looking for is THU312#CP
If you currently have a toilet installed, your rough measurement is going to be the distance from your wall (not the baseboard) to the center of the bolts on the side of your toilet. The standard rough in measurement is 12 inches, with occasional variances of 10 or 14 inches.
For installation I would recommend calling Toto at 888-295-8134 and press 4 for technical.
This toilet comes with a standard chrome trip lever. You can purchase a different finish separately. The part number is THU312#PN or THU312#BN.
The Angle Supply is the part on your floor or wall where you turn the water on and off for your toilet. The only thing needed for installation will be the wax ring, bolts that bolt the toilet to the ground, and the supply pipe. We have a kit with all of these items once you add the toilet to your cart.
The only difference is the flush lever.