Kotaku stated in their May 2nd preview that after a heist mission is done you will be given a report essentially scoring how well you did and how much money you raked in.
Even crazier is that you can change between them all throughout the game!
A special menu allows you to select a character which then takes you up above the city in a Google Earth type fashion before throwing you back down to the person of your choice.
If they don't survive the mission you can keep their cut but they will be dead for good. Planning involves more than pencils and papers, though.
If you want a getaway vehicle in a certain spot you need to place it there. Like many GTA games of the past, mini-missions involve acquiring the right tools before you get to the main event.
Random encounters appear in the form of hitchhikers, police chases, ATM robberies, etc.