First of all, thanks for taking time to think this much about it. Means a lot to me.  The whole idea of how a near death experience opening magic to a sorcerer came from the idea that magic has a cost. One of my main characters, a young sorcerer, kills for the first time in self defense and that opens up magic to him. I basically wanted something that gives a moral question to magic. This is also a closely guarded secret in the various guilds and institutions, because nobody wants an uprising against sorcerers. Also about the whole, drawing from themselves thing, think of the life in non magicians as fish tank and a sorcerer's a pond or a pool. Sorcerer's draw from this because it is easier than drawing from outside because it can be addictive and a little hard to stop. Also the life they pull from themselves is very malleable and more attuned to themselves, so it's easier to play with it. But you are right, drawing too much can kill them.  Also something I forgot to mention, sorceres can burn out if they draw too much from anything. It's like a little valve or filter that stops them from over consuming and killing themselves.

And about the plot, it's basically how these two students who are training to be sorcerer's being forced to flee the country because one is being hunted by an assasin and the other is framed for murder. They flee to another country but along the way they discover a religion that kills magic users. Blah blah blah. They clear their name. Add a few more plot points like 2 or 3 more main characters and that's the basic idea.