Concerning your questions about 3CS gates - the baseplate size of 32x32 is important because then each module hooks up and forms the 32x32 grid.
Examples of the 3CS in action can be seen here:
If the front of your baseplate is extended eight studs, the corresponding baseplate (that sits in front of it) must be also decreased by eight studs. Therefore, keeping to the 32baseplate is important.
However, as you can see from the Festival of the Masters Show (top link) - the outer wall will probably constitute the outer limit of the display, and thus having the baseplates extend beyond might not be that important.
Thus the inner side of the plate must conform, but the outer side doesn't.
My next moc will sit on a 48x48 grey baseplate that adds 8x16 baseplates so it is compatible. It assumes the outer wall will be the outer edge.
Having said that, it is allowed that the wall take any shape you desire, only that the 'hook-ups' meet at the middle point of the 32baseplate. So the wall could bulge out or in as you see fit. Also, there is no rule that it must all fit on ONE 32baseplate.
You could build a wall that sits across several baseplates in either direction. Think of a tetris piece of wall sections. This would allow someone to build a 3CS hill or larger keep, etc.
Hope that answers your questions.
Keeper of the 3CS