Hard to describe without seeing it as you do it, but in essence, you have bark, then cambium (soft and squishy) and then the solid back of your bow. These may be thicker/thinner than other woods, and even vary within the same species so you kind of have to play it by eye as you go. The last piece of ash I worked on had the green/grey bark, then an almost pink/brown layer of cambium and the moment I was through that I saw nice clean white wood which was the back of the bow.
The mora will be perfect for getting the bark off, so have at it with that. The worst case scenario is that you dig into the nice solid back of the bow by accident, but if that happens you just have to chase a ring all the way along instead. I tend to remove all the outer bark any way possible, and leave the cambium fairly intact. As the bow is worked down and moves towards being finished, the cambium either dries and flakes off, or can be sanded/scraped off in time. Or left on! Bows look stunning with streaks of cambium remaining!
As for the use of a drawknife without a shaving horse - I've never had a horse or bench, and I love using my drawknife. A little unusual probably, but what I do is either lean the stave against something and use the drawknife downwards, or more preferably wedge the tip of the stave up against a wall, back up and lower it down until it's just above horizontal. Tuck a towel between the other end and my body, and lean into the stave so I'm keeping it steady, then use the drawknife cutting towards me, as if it were on a shaving horse.
Even better, pick up a cheap Black & Decker workmate, the tool box type with clamping wooden vice lid. You can store all your bow making tools in it, and use the lid to hold a stave or bow fairly rigid while you work on it.
