Hi Yoram,

First I would like to say I 100% sympathize with you.
I'm also an ergonomics freak.
(and a keyboard player, I may add)
I believe that ergonomics is much more important than monitors, mixers, microphones and even acoustics.
If you're not enjoying your workspace, it will never be productive. and you will never make good music in it.
The other factors are technical. Ergonomics is emotional, in a sense.
Now, for your questions: I've consulted an ergonomics specialist courtesy of Kupat Holim. Here is what she told me (with a grain of salt, always):

1. Your feet should always touch the floor when you sit.
2. The top of the screen MUST be on the same level as your eyes.
3. Your arms should be at the sides of your body, not stretched out.
4. Your forearms should be parallel to the floor when you work.
5. Avoid creating a workspace where you have to place your hands in such a way there is a point of constant pressure (e.g. resting your hand on the wrist only) - it'll only cause problems later on.
6. NO matter what people say, split keyboards, so called "ergonomic keyboards", are worthless.
7. Trackballs are much better than regular mice due to lessened arm movement. My personal recommendation: microsoft optical trackball.
From personal experience let me add: avoid thumb-based trackballs.

Most computer desks built today are WAY TOO HIGH.
CHANGE YOUR HABITS or they will RUIN YOUR MUSIC.
I was there, I made the mistakes and I had to pay a high price.

Personally, I would separate the keyboard from the main work desk. Put it on a separate stand, and connect two screens - one on your desk, the other in front of your keyboard. Connecting two mice/keyboards is also an idea.

Hope this helps.
Assaf.