Since he has new fish in there and they can be skittish I would say in a couple days start doing more water changes. He already did a good sized amount and if he does say 3 more of those he should be down into an acceptable range on nitrates.
As far as feeding, I happen to feed everyday, which is not entirely necessary. Many people will skip a day or even two and feed very sparingly. It does make the parameters hold up longer and there will be no ill effects to the fish.
I LOVE to feed my fish, I even feed more than just once in a day. BUT I will drop say 10 tiny tiny pellets in and watch the fish eat them all. I dont throw a hand full in and walk away. lol I make sure every bit of food is eaten. I feed frozen rinsed mysis, brine and bloodworms every other day usually. In addition to pellets I feed flake to my 180g since I have some smaller fish in there like chromis and the blennies.
The trick is to feed a varied diet in moderation. When people see my fish the usual first remark is that they are fat. lol Whether healthy or not I do not know, but it makes me feel good that my fish are fat, kinda makes me feel like I am doing a good job.
And finally, I do HUGE water changes on my tanks. Sometimes more than 50%, depending on the tank. That is how I think I manage to keep my tanks ok with the amount of food I put in. I also run good skimmers which pull ALOT of organics from the water.