The Simple English Wikipedia aims to use about 1,500 words, so that might give you a sense of what's possible. That said, if you look at it it's clearly unnatural and contrived; most people you talk to aren't going to be able to restrict themselves to the right set of words (and even then it can be dicey -- you can know all the words in the phrase "put up with something" and yet have no idea what the phrase means). https://simple.wikipedia.org/wiki/Main_Page