The cuben is not recommended for shelters with stoves. You might want to consider a pyramid, if you want to have the shelter as light as possible and fit the most guys in as possible (tipis have a lot of gear space that only small pieces of gear can be placed but are otherwise unuseable areas in the shelter for people use). You will also want to have tieouts on all of the walls about 1/3 to 1/2 of the way up to increase useable space.
Also, tipis without stoves suck in cold humid climates, because they are hard to ventilate to prevent condensation, whereas pyramids are really easy to pitch up off of the ground to ventilate on one side, or all of the way around.
For sizing, having used a few pyramids myself of various sizes, for 3 guys and gear, with a small stove, I would make the pyramid the same length as the BPWD Luna 4, but make it about 1 foot wider (and put the door on the long side so that everyone can enter without climbing over each other) and put the stove pipe opposite of the door, with the stove thus out of the way of the entry and out of the way of sleeping spots. You might just want to look at the Seek Outside and BearPaw Wilderness Designs Shelters of that size (the Redcliff and Luna 6 I believe) and see if it is worth the hassle to make one. Also, I bet BPWD would make you a Luna type shelter to any specification/size that you want.