how much of an impact do you think the man himself, and his co conspirators actually had in the grand scheme of things?

Aside from giving the Austro-Hungarians an excuse to start a war with Serbia, their impact in the grand scheme of things was not great. Berchtold and Hotzendorff, the Foreign Minister and Chief of Staff of the dual monarchy had already decided in 1913 that Serbia must be crushed if the Empire was to continue to have a future as a Great Power and as a player in the Balkans. Even if the Archduke had not been shot, Princip's conspirators had already lobbed grenades at him, and a few had been captured. That alone would have probably been enough for Austro-Hungarian leadership to demand a reckoning, though the Archduke might have been a counter-balance here.

EDIT:

Thomas G. Otte's July Crisis is an excellent read for the crisis as a whole. Tim Butcher's The Trigger is a good read for info on Princip himself, even if it's more pop history.