If he's come into your home straight from rescue today he's bound to feel very unsettled by the experience. I'd just ignore him for a few days whilst he adjusts to your routines. By that I don't mean you should be harsh and withold attention but just leave him be for a while. Don't ask too much of him and do give him access to quiet places where he can go if it all gets a bit much for him.
It's a lot for a new dog to learn, and eating in the company of strange dogs can be very difficult. He isn't likely to understand why he can't look at the others bowls and if he's hungry he'll be even more motivated to stick his head in there! Be guided by him and also by your other dogs to tell you if they are ready to eat nearby, some people have to keep dogs separate for every mealtime and until one of your dogs tells him not to he'll see no reason why he can't eat their food too

Actually I'd take it a positive sign that he is willing to eat at all on day one. I've known dogs that just won't ever eat in strange houses or in front of others.
It's much too soon to label him food aggressive but you're right, he may need some boundaries. However, I'd caution against too many rules too soon - give him a chance to get to know you, and for you to observe him. Whatever you see on day one isn't likely to give you a true picture of the sort of chap he is. Far from being grateful to be rehomed some dogs get very stressed and good manners go right out of the window...
Good luck with him and well done for taking him on
Kindness is the language which the deaf can hear and the blind can see ~Mark Twain