"Where should the groomsmen hold their hands when they are standing at the altar?

This is a decision to be made by the Bride and Groom.  Either together in from of them or on the side, but never, ever in their pockets!

"What buttons do I button on my jacket?"

Well the rule of thumb with the men's jacket is as follows: Starting with the top button - it is Sometimes, Always and Never.  Which ever the groom decides is how the rest of the men should follow suit.