You can combine them, but they are different things.
Smoking - indirect heat. On a vertical smoker you need heat diffuser between the fire and your food. On offsets, spend the extra on a reverse flow so it is far from the firebox. It's just like roasting in an oven. I've even made cupcakes and bread on a smoker. Aim for like 325-350 for poultry to get the skin to render.
Rotisserie - direct heat over the fire and you need it to rotate all the time to cook evenly. The fats drip right down into the fire and burn making awesome smells.
If you do option #1, cooking with indirect heat, the heat source is even already, you don't need to spin.
Getting the rotisserie setup is definitely space consuming as far as capacity goes you can't cook as many chickens at a time. What kind of volume are you thinking?