What's the hurry? Let the furniture be delivered and see how it sits in the room. I feel the best rooms come together when you can see the bare bones established and the room starts to take on its own personality. For me, that's the most satisfying point--where I know instantly whether or not to purchase something because the room is now dictating the style. It's JMO, but I feel the biggest mistakes most home owners make is to try to pull things together as fast as possible without taking the time to ascertain how the room is taking shape over time.

One reason to order the chair now (at the same time as the other chair) is that you would be getting fabric from the same dye lot. It is possible that there could be slight variations in color from fabrics from different lots. That said, if you've got matching sofas, you might consider mixing things up a bit with the chairs? Good Luck.

I'd wait as it may be just right and you don't want to have regrets by buying one you won't use. It will look beautiful with the three pieces and, if need be, you can buy another later. Personally, I would just use the "one" chair. I think the 3 pieces in leather is enough.