If rests are desired then these should work fine, one on each hand tucked in right in front of the keyboard.
Yes - you can add your own off-the-shelf wrist rests. The cons are that you have too many individual parts on your desk (especially if you have several other input devices/gadgets/whatever on your desk, like you had mentioned you do - I do too).
It'd be great if the DOX came with optional/removable palm rests - like the Truly Ergonomic, for example (looks like they did a good job with that - but I've only seen pictures). But I know this might be asking too much from Dox.
Halved keyboards however, allow you to dynamically alter your ergonomic situation on a whim.
Exactly. I like split because I can change my position at my desk throughout the day. I'm often at my computer all through the day, with a sit/stand desk. It's great getting to move the keyboard halves around
on a "whim" to accommodate different positions. This really makes it feasible to be at your desk all day with a middle age body (heh) and not suffer (and in fact, enjoy it!).
I tried a split keyboard that was good for changing positions through the day - that was great. But it was still missing other features I wanted (mechanical, and matrix layout).
Another thing I like about the Dox is it looks like it doesn't have dedicated Function keys. I'd prefer Function keys on a separate, flat keypad/keyboard. (But the drawback is one more separate, corded device on your desk).