If it is really a tiretrack eel, then yes, it will get 3 feet long or so. If it's been mis-labled and is actually one of the smaller spiny eels like zig-zag or Zebra eels, then they should only reach 18"-24". We'd need a good clear picture of it to tell.
And as for needing more tanks for more cool fish... Oh yeah! I have 5 tanks in my livingroom right now with various tropicals, and I'm expanding to african cichlids in the next month or so, and Have plans to set up a birchir tank (with eels if I can get them, too!) over the summer. For an expensive hobby, Aquaria is way, way too addictive.