Puppeteer is pretty much right, we aren't really releasing a lot of information on the Dragons.
The half-orcs you referred to we call Drakes. Drakes are foot soldiers and laborers, they cannot fly, they cannot breathe fire, they have no magical ability of any kind. An image has been posted elsewhere, but here it is again:
Yes there are flying units, currently we have 3 planned.
Currently only 2 units can breathe fire, you could in theory destroy an entire army with it. However fire breathing dragons aren't the trump card in the game, it's not like picking dragons and building a bunch of fire breathers is the ultimate way to win, we will be balancing them out to make playing other races just as effective as Dragons can be.