with regard to the subtopic - left/right mouse keypad etc.
For what it is worth -
I am right handed. I use a Kensington trackball with 2 keys + an Ortek USB ergonmic keyboard with a built-in keypad on the right side.
To solve this problem, I have added a USB keypad and positioned it to the left of the keyboard.
However, the greatest asist to my efficiency is the use of a trackball rather than a mouse.