(
Dvorak user here -  so sorry, I'm not a veteran Colemak user.  I have tried a couple of Colemak typing exercises though, and I personally found it was quite easy on the right hand - compared with Dvorak.  If you look at the Colemak layout, there's quite a bit of punctuation there.  You'd probably avoid the pinky stresses of Dvorak, especially with the backspace moved.  Using the right hand more might be a surprise for Qwerty users that are already used to the left hand bias.  The vowels are mostly on the right except for A under Colemak.  Dvorak on the other hand places the vowels on the left side.  Actually my left hand feels a little underworked but I'm happy as a right hander with that.  The left hand stagger of the keyboard looks worrying to me.

I've shoulder/neck issues on the right hand side brought about before I shifted to an alternative layout.  I haven't used a mouse on the right hand side for getting on ten years and the stresses and pains in the shoulder haven't abated all that much.  In fact I'm  not even that convinced the mouse had that much to do with it.  Having the mouse on the left evens up the keyboard a little,  I can line up the numeral 6 with my naval.  I think my issues stem more with general posture at the keyboard, and the result of desktop hopping from the old days of technical support.  Personally I find conventional touch typing quite stressful in that it's quite an alien position for your arms to be in, combined with pressing down.  Advocates of vertical keyboards tend to suggest we are better extending our arms in a hand shake position rather than the whack a mole posture.  But I guess a million drummers might disagree.  I expect pianists to suffer also, but perhaps they are more expressive and less restricted, having a little lateral movement.
)

Dvorak was developed in a time before computer mice, so it places more load on the usually stronger right hand. I thought Colemak didn't overload the right hand so much? Anyway, the balance should be acceptable even for Dvorak (and if it isn't one could always switch the mouse hand I guess).

The Wide ergonomic mods take a lot of load off the right pinky (but gives it to the index finger or fingers), as do the Caps->Back or Extend mappings (but they give it to the left pinky). This gives you some flexibility to find something that suits you, regardless of basic layout choice.

> ...getting capslock to work as backspace on OSX...

That's worth asking as a separate thread/question under 'technical'.