Why are console video games played with a controller or a touch screen, and not a keyboard? Because those are the best-suited input devices for the way most users interact with their device. Guess what? Being a digital painter means you're no longer included in "most users". Now you've got a different set of needs, and will most likely be spending longer at your computer than the average user. With this in mind, a standard keyboard might not be the best input device for you. Just like using a stylus instead of a mouse, you might want to consider alternative keyboards or controllers for your other hand.
When it comes to ergonomics, re-mapping your keyboard shortcuts is a great start - but it doesn't need to be the end. Over the years I've radically changed my input scheme and the results have been very clear: expensive, but worth every penny.