Alright, a couple of things. It takes one standard action to activate all energy enhancements on a weapon, regardless of number, assuming the weapons creator wasn't being odd. The "burst" effect of an energy burst weapon is always on--that is, no matter what preparation you've done, roll a critical hit get the extra damage. The damage from the "burst" is in addition to the regular energy damage, assuming you activated the regular energy damage prior to the crit--this is a distinct change from 3.0. Finally, in most cases, energy burst weapons suck. You generally get more for your money with plain enhancement (+2 gives you a +4 damage on a crit, always +2 on attack, no resistance applys; energy burst weapons give you an average 9 damage on a crit, no bonus to hit, low bottom roll of 2, and they don't effect all creatures). It is fun on my Falchion, where I have Improved crit and Power crit, but not great.