I only pull adult dogs for rescue and find them very easy to work with/train. There is a thread in the rescue section right now that I started (What to do when bringing a new dog home) that you might find helpful, although it really is a bare bones outline...do a search using the search engine on this site for food aggression and anything else that might concern you
Leashing a dog to you allows you to set the rules in a non-confrontational way....and it is important that your dog understand that you are the one deciding what is appropriate behavior in your home...again, check out that thread.
I had a foster who was fine around his food...when he adopted, the husband felt he needed to show Zach who was in charge, so started putting his hands in Zach's food bowl while Zach was eating...what he ended up with was a food aggressive dog because by doing that, he convinced Zach that his food needed to be protected. Don't pick up his food bowl or mess with his food...if you want, casually walk around near him while he's eating (but far enough away that he doesn't become defensive) and toss him random treats...convince him that good things happen when you're near...certainly the easiest way to deal with this is to simply leave him alone when he's eating as others have mentioned.
I paid a trainer for three one-on-one sessions with Zach as he had a much more dominant personality than I was used to...and it was well worth EVERY penny. These weren't traditional obedience classes, but rather the trainer showed me how to interact (or not interact in the case of him jumping up on me!) with Zach...how to trade-up, how to establish control of an alpha dog in a non-confrontational way...and boy, was it an eye opener....and I would guess many trainers would reduce their fee for a rescue (mine only charged $75 for all three sessions).
I'm not clear in what other instances he's growling at you so can't offer anything there.
Here is a link that provides a search engine for trainers in your area...best of luck...hope things work out.
Association of Pet Dog Trainers - Dog Training Resources