Don't rush into things, especially with large monitors. Make sure the one you have is set up nicely and is eating well for a month or two before you even think of shopping for a new one. (If you must, set up a new tank so that when the time comes you are 100% ready for a new lizard and just have to go get it.)
Research as much as you can about a specie before you get it, you should know all the basic husbandry needs onew the fly before getting it.