Im using P mode, A mode and M mode.
Whatever mode you use is really depend on the situation, and your shooting styles, you have to understand all the metering methods your camera have, and integrated to your exposure mode.
Your goal is to capture the moment, and product decent pictures to the wedding couples, so you think of use whatever it takes to achieve this.
For what to wear during wedding assignment.....................
Do wear something comfortable and presentable
Dont wear something outshine the couple
Dont wear a pair of tore jeans with many holes
Dont wear Tees and Bermudas.
Dont wear sandals or slippers
Dont wear a pair of socks with holes
Dont wear a pair of shoes that you need more than 1 min to put on.