I don't know if this is an option for you, but you might want to start out at an unreconized. Its cheaper and ususally more relaxed. I think everyone else has everything covered.
I have a cheap intec flex. Its OK, does its job(:
I do woof boots on all four, and bell boots.
Make sure your horse is in good shape(:
Double check that your bit is legal for dressage, and know your test like the back of your hand!
If you are from the hunter world, I suggest reading the USEF rulebook for the rules on tack(no standing martingales and all that jazz)
Eventing is SO MUCH FUN! Be careful, have fun and watch out...because I have a feeling you wont want to go back to the hunter ring :P