I would question whether his food obsession actually stems from being starved, or if he's just a piggy food hound who has your number. You'd swear some of mine are currently starving, the way they'll try to dive for grass on a trail ride, but it's just a bad habit that has to be broken. Demand his attention and his respect, period.
Longeing--personal preference. I always used to start with the horse free in a small round pen, but nowadays I'd just as soon start in the open on a longe line. Use the whip to direct him. Don't be afraid to pop him with it, but of course not beat him, if necessary to get him moving out.
Once you establish some of the above, and have him well halter broke and responsive to pressure, the trotting in hand thing should come naturally.
Took the words right out of my mouth. :P
My rescue pony was the same for food, he'd get a flake a day if he was lucky before I got him. He'd get stressed and upset if you went near him when he was trying to eat (Used to get beat with things when he was fed) and when food arrived he'd take every opportunity to just mow down as much as possible. Over time he got over it. He loves being rubbed when he eats now though if he doesn't know the person he might pin his ears at most. He also isn't as crazy frantic about every little thing of food, but does get quite excited for supper. xD It'll take some time for him to settle in and realize the foods not going anywhere. He could just be a bit of a piggy pony like said, but over all, I wouldn't overly worry about it and just give him time. :)
As per lunging in the round pen I always start horses without the line first. If you have a lunge whip you can send him with that, or even if you have rope you can also use that to. I'll see if I can't get my friend to take a video tomorrow of me lunging Shnook to help give you some extra tips on starting a horse to lunge. When you send your horse on its "bad way", make sure you're not getting in front of the horse if you want it to go forward. A trick I was taught was when sending the horse out, have your belly button face a little behind the girth area. When your horse is out and at the pace you want you want your belly button to face the girth area. When you want your horse to slow or stop face it more near their shoulders. When starting a horse into lunging, it's important not to get ahead of them. Otherwise they may (and most the time) take it as you blocking them from that direction. If the horse is following you then you're definitely far too ahead of your horse. Don't get behind your horse enough to be in kicking range, but you do need to make sure you're a little behind the girth area to send him out.
As for teaching your horse vocal commands, ask with your body language and pressure/whatnot but also start saying what you want the horse to do when you ask it with the rest of you. Keep doing it and with enough time and work your horse should know what you expect by vocal commands.
Hope this helped! :)