Do what ChuBerry said....listen to some players and choose which one you like the sound of better. When you do buy a horn, go someplace where you can try out a few, and the staff is friendly. Talk to some of the local musicians who teach if you can, they can probably help you out, plus give you lessons if you're interested. Get the Standard of Excellence books, but you should also find a good teacher, even if it's every other week or something, to help you grow and make sure you're playing the correct way, and not developing bad habits. As for a mouthpiece, I'd say start on a Selmer C* or something similar. This isn't the best mouthpiece for jazz, but it would help you to start here, and once you can get a good sound with it, then move to more of a jazz piece.
If you're set on diving into a jazz mouthpiece, check out some Meyer's, Morgan's, and Otto Link's. Start on the hard rubber pieces, not metal.
Good luck finding a horn. Be wary of cheap horns that won't last, spending the few extra $$$ now could mean fewer issues with a horn and more fun playing.