They get confused, they look for help, they pump the GM for info by quizzing every contact they can find about anything they can think of. Hours go by with no conclusion other than planning is hard. Players get bored and pick fights with random cops. However, most gammers do not have this patience. If a movie had all this library research and long night recon the audience would go home before things got interesting.
Most movies start with the action.
The plan has already been done, or it is done behind the scenes. I recommend you let someone other than the PCs do all this research and planning. This can lead to roleplaying situations where the PCs disagree with the plan, but must follow it or forfeit their payment. The plan may even look like a trap, it might even be a trap. Therefore, the PCs must still react to unforseen events.