I 100% this when it came out and I don't recall there being any controller input hints when playing with M&KB. Try aiming down sight with weapons etc, should help with headshots.
Thanks for the tip about aiming down the sights. I didn't know there was a different way of doing this other than the "ready weapon" right mouse control. After trying all my assigned buttons whilst readying a weapon, though, I found the "binoculars" binding let me aim down the sights! I must have missed the tutorial for this too and wouldn't have guessed that was the way to do it. But, great - headshots are go!
I checked before work this morning, and I definitely do see the odd controller input (at least I think that's what it is). When running from the first village, for instance, a prompt came up with an icon depicting what I can only assume means pressing down on the right controller stick to whistle for the horse?
I'm still not sure I've got everything down with sneaking behind guards, either. I can throw them sometimes, but I'm not sure what triggers that as it seems to work with my left click, but sometimes left click doesn't do anything. Googling this it looks like it might be triggered by left-click plus a direction movement? As I say, I missed the tutorial for this so I'm not sure what I'm doing. It's annoying that 95% of Google hits for this game only refer to controller inputs, but I guess that's to be expected since even most PC players probably use a controller.
Also finding the camera makes it a bit tricky to spot enemies I've not marked as I move around obstacles, but I guess I'll just have to be more careful about reconnaissance.
Thanks to your hint about aiming, though, I was able to clear the first little area very easily, so thanks for that! Actually enjoyed the few minutes I played before work. Onwards!