It has been a while since anyone posted on this, but I want to put in a few cents worth about standardizing. If you try to seek and use an existing standard, you will probably end up with less than you desire for economizing spaceflight. The Arianne card cage packaging standard is an example of how to start, though. Begin with what your payload needs to be, and modularize out from there. (i.e., a human capsule, 2 human capsule, etc,, then to cargo compartments, control systems, actuators, and finally, to the hull. By working from a team concept (you may be all the members, but play different roles), you should be able to come up with a highly integrated complete spacecraft that is mission-flexible. Don't get caught up in fear of doing it 'wrong'. If you get it right, everyone will look to your design to find out what is 'right'.