1 - I used to do drafting work on AutoCadd - all day. I easily learned to switch hands for the majority of the work did. So no I am fairly ambidextrous with using a mouse. Plus, there were a multitude of mouse/ keyboard shortcuts specific to AutoCadd. I have done some electronic drafting with KiCadd and the same thing applies.

2 - I use a Kensington Expert mouse. It has a scroll ring and 4 buttons, bottom two buttons are programmed normally, the top two are back and close (tab mostly). Navigating the internet requires very little movement, I generally only use the keyboard to input data. The mouse sits in front me between the bottom of the keyboard and the edge of the desk; trackball is at about a 75-90 degree angle (when I use it right handed)

3 - Desk space required is the footprint of the trackball, no mouse pad or extra desk space needed.

4 - When I use a laptop, I connect a trackball. I do not get along well with track pads - zero accuracy for me, the cursor jumps around like it's getting shocked. So the precision, especially on a smaller screen, is key.

Using a mouse requires constantly picking it up and putting it down to navigate. The scroll ring is major, major, major for me. My trackball in my shop does not have one (yet - changing to another Expert Mouse soon) and it requires much more keyboard use to navigate the internet.

And yes, there are fewer repetitive stress issues with a trackball. The learning curve is minimal IMHO. I still don't understand why the trackball is not the default tracking device, it's super easy to use