Okay, in short, you should look into a 20 gallon (long) tank. The bare minimum is 10, and I keep mine in 15 gallon tanks, but if I had space I would upgrade to the 20 long so they have more walking room. The water needs to be kept cold, they need sand so they can walk (also live plants are very nice), and I suggest CaribSea Super Naturals white sand. I used to use Imagitarium before I found out it was actually just plastic, and the black sand has harmful dyes that never really wash out. Never use gravel. Axolotls eat whatever fits in their mouth, and what ever is smaller than their head, but not small enough to be passed if they eat it (like sand) should be kept out of the tank.
As for feeding, live food, or at least food that can pass as freshly dead (like frozen) should be fed. Earth worm is preferred because it is highly nutritious and will not stunt their growth, but make sure you change up their diet because like humans, they can get sick of it to the point of throwing it up in the tank because they have become so tired of eating it.
I literally have several pages in word typed up and categorized if you want a more in depth guide, I'll start uploading it to the thread.