doesnt notice the food? is he heating? not eating isnt a good sign, not an indication of tank conditions but of illness. Next time you feed check to make sure he eats.
Whenever your ammonia and nitrite levels are 0 then you can add more fish, but remember to add them gradually, one or two a week. If today is the second day i'd say you have another two weeks to go before your cycled at least. I know its hard not to buy fish to soon lol, but trust me when i say its worth the wait. Patience is a staple in this hobby.
If you add fish to soon you can restart the cycle itself which would make it take longer AND add stress to your fish which could kill them, last thing you want is to add a fish to soon while the tank is cycling and then the fish get stressed and get ick, then have to treat ich in a cycling aquarium and have to wait atleast 2 more weeks after that for hte ick to be gone.
So short answer- when ammonia and nitrite=0 ppm