I recommend doing a ton of research, Night. They require very specific water parameters and substrates. Temperature of the tank is the biggest thing. Depending on where you live, you may want to get a chiller which tend to be at least $300.
You should be good with a 60 gallon tank as long as there are enough hides for both of them and they are the same gender. Do not house axolotls of the opposite gender together.
My axolotl is spoiled with a 75 gallon tank. 55 is definitely big enough but keep in mind the tank should be longer than it is tall. They require a minimum of 29.5 gallons for one axolotl