A small juvie I don't see a problem with to start. As it gets bigger it maybe a problem, especially all alone. Your tank size is important here as they are territorial. They may not be prone to eat the other fish, but as it grows larger - up to 9 inches - it could still do damage to other fish simply by its size along. Give it a little room and a piece of pvc pipe to hide or somthing and they are very peaceful fish. Some can even be hand trained.
They are pretty intelligent fish and definately prefer to have the company of others. Many people keep only a single one, but you are better keeping them more like five together. Don't try just two as you will end up with a dominant one and the sub-dominant will likely be picked on to death, but if you have about 5 this aggression will be dispersed amongst the group.
Of course, if you go for a group of 5 then you will need a nice size tank - so part of this answer depends on the size of your tank. In fact, even if you decieded to try one, your tank size would be important. So - ie what size tank are we looking at. If we are looking at anything under 30 gallons I wouldn't be bothering with considering a single one - bigger, perhaps...
Also, be sure to use a cover which is EXTREMELY secure. These guys are escape artist - especially if kept solitiare. I have heard of people stating that they have managed to squeeze through cracks FAR smaller than they are. This is another reason to have multiples as people have reported less of a tendency to make escape attempts when company is present.
A few possible options for all the Mollys, Tetras and Platy you got with the tank for free would be to rehome them or even see if your Local Independant Fish Shop will give you a little credit on them (though it won't be much). I think a species tank with all Elephant Noses would be a marvelous tank to have. Now you've got me thinking!
