Brand new...what do I need?

You'll probably be given a swim cap--races usually give each wave a separate color. although it might be a bit different with a pool swim.  See if you can get in touch with the race director and ask.

Socks or no socks is mostly personal preference.  Without is faster in transition since you don't have to put them on, but some people aren't comfortable without socks.  I usually skip the socks on the bike (I've only done open water swims, and don't want to put socks on over sandy feet) but always wear them to run (some people don't--again, faster).  Just be sure to try sockless in training to see if you're comfortable.

You certainly can use running shoes & platform pedals with or without toe clips, and that might be your best bet for your first race.  Once people get into the sport, clipless pedals and cycling shoes are usually one of the first equipment upgrades.  It really does make you a lot more efficient.  But again, make sure you train with them before you try to race with them.

Take a look around the site, there's a lot of info already posted.  There's a really good thread recently started in the Triathlon Talk forum with FAQs that will probably take you to the answers to most of your questions.  But keep asking--people here love to help.