Your boy is very handsome, that head is gorgeous! Gotta love the nobility in the look of those old lines :)
As for weight, when we're working our horses we feed them a mixture of beet pulp, mineral, power 2000 and sunflower seeds (black) twice a day in small portions...about a scoop each. It seems to work and hold really well for them, although some people disagree with beet pulp, we've had really good results with it, i think the main thing is that whatever you choose to feed him consistency is the key for horses. We've had some boarders come through and feed their horses big bows of feed once or twice a week, but i saw absoutely no difference in their horses.