I'd recommend getting familiar with the rules, first, before running ANY campaign! I'd also recommend B1-9, In Search Of Adventure; by the time you finish B4, your Players' Characters should all be at LEAST 4th-6th level! (You can get the originals, if you have them, or the well-packaged supermodule that included ALL of them in one neat "mini-boxed" set, along with a sidebar adventure to run, as well!) U1-4 is an excellent way to "build-up" your Players' PC levels, as well; Saltmarsh is both easy, yet provides plenty of challenge for even a veteran!