1) For discounts, try broadwaybox.com, where you will find discount codes for many shows. Those discount codes can be used at the box office, telecharge, or ticketmaster.
2) Depending on the show, you can often appreicate the effect of production numbers and set designs if you are away from the stage. Plus, some stages are very high, so seeing from the first couple of rows may be difficult if you're short.
3) No dress code, but I would recommend nothing sloppy (old jeans, t-shirts, etc.).
"It does me no injury for my neighbour to say there are 20 gods or no god. It neither picks my pocket, nor breaks my leg."
-- Thomas Jefferson