Since it's supposed to look like gifts, and most gift boxes aren't necessarily 4" tall, I was thinking of just making at least a couple of the cakes as one cake that is torted, and maybe the rest as 3 layers (consisting of one full torted cake and one layer of another cake that was torted - so it would be like 1.5 baked cakes instead of 2) Does this make any sense? I just picture the boxes being way too huge otherwise - not like elegant gift boxes.... The top little box could be the full 2 regular layers height,.... And for the remainder of the servings I will just make a regular 2 layer sheet cake.
And then I would just figure the serving sizes according to how tall they are. I will be cutting it anyway, so I'll know.

Is this what you would do?

Your cakes are going to be 1.5 layers (torted) instead of 2, correct? The height won't make that much difference in the number of servings, unless you want to cut them a little larger than standard. Most people would be happy with the standard 1" x 2" even if it's only 3 " high.

Since you'll be cutting the cake anyway, you can do it however you want.