you should have someone come in once a day just because you will be gone for so long. Cats don't like being abandoned that way and four days is fairly long. Might be ok with some other cats in the house with them, but not totally alone, not the first time.
Cats aren't dogs that will gobble up every last morsel as soon as you put it out. You can put enough food and water out for the time you will be gone (with some excess just in case) and the cat should be fine. I've been doing this for years, and 2-3 days is not a major problem. Longer, and I like to have someone stop by and play or just be around the cat or cats. Make sure everything is ok.
The cats always know when I will be away because they see my pack or bag, and see that I put out extra food. They are used to it. Been a long time since I only had one kitten that had never seen me go away before, though. They tell each other somehow when you have more than one cat. The behavior of the cats that have been through it before somehow calms the one that is only seeing it for the first time.