A 120 gallon tank is a great size for wolf fish. They are very messy, and they really don't do much other then sit still waiting for prey. They prefer a very dim/dark tank with tons of floating vegetation (go plastic, I assure you on this one), so even the tank itself won't be much to look at in the conventional sense. As long as there are plenty of areas to hide from one another, I've had little problems with more than one fish in a tank. Tankmates of other species, however, are not an option in my experience. Mine ate everything in the tank when they were still juveniles (about 5-6"), including fish larger and toothier than themselves. These fish are best suited for species tanks, without a doubt.
All the above being true, I absolutely love them and will probably always have at least one in the collection. Enjoy.
BTW- Mine were rather easy to convert to eating shrimp (just buy a bulk frozen bag from the grocery store and defrost a few at a time for feeding). It's cheaper and safer than live foods.