Nippy could be teething, which should stop.
If its becoming a habit, a sharp 'no' and point your finger at him. Don't smack/tap his nose. Dogs noses very sensitive, hence why if you smack, they bite ! Short, sharp shock noise works best.
Sounds good what you're doing with the food. You can also help that by getting soft, chewy biscuits (hi-life is one brand) - mix a few in with dinner, makes them work a bit at eating.
He might be a bit young for Natures diet or similar yet. If you get a really good quality meat, like ND or Fish4 - there's loads, you can save pennies on biscuits - or buy good quality biscuits in bulk ! Feeding wet & biscuits usually helps them not to wolf food down.
Or, you can get feeding bowls to help. They're sort of knobbly, so they can't wolf grub, they have to get inbetween the knobbles to their food.
Bonnie is very barky. Collie trait, they love to talk. She most specially loves barking at pigeons, silly cow, who aren't fazed by her at all.
We get red kites here. She ducks at them !
Lead training...perhaps try a flexi one ? Lots of control & can keep him close, but let him run when you want ?
We walk Bonnie on a harness & long flexi. Keep her close on paths etc. I taught her to sit & wait at crossings too.
If she ever forgets I ask her "what should you be doing" ? and she does it !
It always feels like such a long time & load of hassle when they're little. You get the payback when they're older. 
Tell me to eff off if you know all this !