DJ or a band is really up to what your wedding is like. What's the age group of your wedding crowd?
DJs are great as they run the show for you. The MC works with the reception hall and coordinates all the important times throughout the night (first dance, cake cutting, etc.). A band does not do that for you and you'll need to find someone to 'manage' the night.
Lights are optional, really depends on where your reception is held. If it's a classy banquet hall, you'll probably want to keep the lights to a minimum. If it's a large hall, you may want to spring for more lighting equip. It really boils down to what type of reception you plan to have.
For my wedding coming up in June, our DJ/MC cost us $3000. This is in NYC, where everything cost more than anywhere in the US.