Basically, my line of thinking is that no matter what, I'll have some kind of squishy wrist rest under my hands--the built-in wrist rest basically just determines the height, and whether I have one big one (no rest) or two small ones (rest). Also, one thing to consider is that Ergodox enables you to have your two halves spaced as far apart as you want, so maybe the two-small-pad method is best; in that case the design with the rests is best. it's worth noting that having the pad sitting on the case's built-in rest keeps the pad in place relative to the keyboard, whereas the case without the rest could potentially scoot away from the rest or something.
Food for thought.
I think it's best to have two seperate wrist rests/pads. And as you said, if you use seperate wrist rests, they might move around etc. (Of course depending on the wirst rest.)
This is why I will go for the Full hand option, although it looks not as cool.
For those people who want to buy extra PCBs, may I ask why?
Do you use it for backup if you screw up or do you want to make more than one keyboard? If the latter, why? And where do you get the other supplies needed?
And one last noob question: if I want to change the switches later on (because I have no idea which I want, will be my first mechanical keyboard
), does it mean I need to unsolder all of the switches?