What causes RSI is mostly centered around tendon and their sheath tension.
For example, if you use a straight keyboard (don't! Ergonomic all the way!) that is raised toward you as opposed to away from you, keeping your hands on that keyboard for multiple hours in a row without ever reaching for the mouse is pretty much guaranteed to give you RSI. Reaching for the mouse will actually bring relief to your tendons.
Another keyboard habit that will put a great deal of stress on your hands and wrists is leaving the Control key at the bottom left of the keyboard. Typing a control key with this configuration will bring great stress on your pinky and other tendons in your hand.
This was 10 years ago, but I remember reading up and something with the forces enacted on your tendons moving the mouse around were exponentially worse than typing on a keyboard.
I use a touchpad when possible knowing that, but I've never double checked myself. Anecdotally, I've only developed RSI in my mouse hand from gaming (same story for my friends who game as well).
One point to add to all of the great points here is consider getting a smaller keyboard (or an ergodox) especially if you're on the smaller side (for the same reason as the last point, stretching less tends to be nicer on the tendons).
I'm not saying RSI in your wrists, that's mostly on straight keyboard (dacman all the way folks), but I personally had pretty bad RSI in my shoulder from the keyboard-mouse switching.
What causes RSI is mostly centered around tendon and their sheath tension.
For example, if you use a straight keyboard (don't! Ergonomic all the way!) that is raised toward you as opposed to away from you, keeping your hands on that keyboard for multiple hours in a row without ever reaching for the mouse is pretty much guaranteed to give you RSI. Reaching for the mouse will actually bring relief to your tendons.
Another keyboard habit that will put a great deal of stress on your hands and wrists is leaving the Control key at the bottom left of the keyboard. Typing a control key with this configuration will bring great stress on your pinky and other tendons in your hand.
Recommendation: map Control on Caps.