Here's a
link to a post on modular wall building that was cut/pasted from our listserve with a few more variations on this theme. In the archive thread I explain the system I came up with that we use and can supply some drawings or pictures when I'm back at work tomorrow if you want.
A lot of good ideas in these posts, it's great to read! I've also used MDO for its light weight and paintability for previous wall builds, and have used a variety of cam locks and just plain ol' brackets to join walls together. It's all interesting because everyone develops something unique given what they can with what they can manage within budget, time to build and/or change between exhibitions, gallery space limitations, ability or inability to move and/or store walls, floor conditions, skill levels, modular needs, etc. You have plenty of enthusiasm which goes a long way for a daunting project like new walls. These probably won't be your first set of walls, there isn't a wall system that can't be improved somehow. Good luck!