I developed RSI from typing up long equations and calculations in TeX on a German keyboard layout with Emacs. It was a nightmare.

I switched to Vim, and a Dvorak layout. I really like the feel of Dvorak - every time I have to type Qwerty for an extended amount of time, my hands get uncomfortable.

I also like modal editing. You cut down on the amount of key chords you need. I've since switched back to Emacs with Evil.

Another trick is to implement some break routine. A typing break of 30 seconds every five minutes may already be enough. There are many tools ta enforce these. I used the venerable Workrave, but it's ancient and has bad UX.