As an epilogue to Guns of August, I would suggest reading Richard Fromkin's Europe's Last Summer. He builds on Tuchman quite a bit, but had access to new archived material (as it was written decades later, after the fall of the Iron Curtain), so there's a lot to add. Despite being history books, both are remarkably gripping reads.
Yes, here is the extension Fomkin makes, in a nutshell. You say of GoA: Which I would agree with. Fromkin uses his archived material to show that the calcified alliances were what set up the conditions of unnecessary war, but that one singular man, von Moltke, was almost entirely responsible for precipitating it. It shows that in the right place at the right time, one man can have dramatic effects on the world.Basically outlines, in gripping terms, how a calcified alliance system and the crumbling remnants of the Hapsburgs brought about unconditional European annihilation despite everyone's best intentions.
I don't think you'll be disappointed. When I get off my current fiction kick (I tend to go back and forth in long stretches of only reading fiction or non-fiction; I don't know why I do that), I plan to read his A Peace to End All Peace, which also might interest you, because the subject matter is the creation of the modern Middle East, a subject that you appear to have read at some length about.
interested third party here I did some googling and couldn't find a satisfying answer to what Breslau as an event means. Was it the siege of Breslau in 1914? Was it the name of a ship that Tuchman witnessed as a two year old?