I believe the question on a German atomic bomb has already been answered on here. I just wish to make sure the general consensus is that they were not very close to an atomic bomb.

The Germans never got close to an atomic bomb at all. They had a small, exploratory nuclear fission program that spent most of its time and effort trying to figure out how to make nuclear reactors that might be used for military propulsion, and they never got any of them working.

As for historical inspirations, the Germans did pursue several very high-tech Wunderwaffen, the most significant in popular culture being the V-2 rocket. The V-2 did not have any great effect on the war effort — in fact it was so costly to the Germans, and inconsequential to the war outcome, that some of the Allied scientists secretly welcomed their use — but it did have important postwar consequences, and it fueled the reputation of the Nazi regime as pursuing unusual technological outcomes.

I'll add some perspective on one secret weapon--the V-2. Martin Van Creveld gives some analysis in The Age of Airpower.

Developed by the army, the [V-2] was a magnificient technical acheivement but owing to its inaccuracy and the relatively small warhead it carried, it never justified the vast resources invested in it. (page 117)

Starting in September 1944, about 3,000 of the missiles were launched at targets in Western Europe and Britain. Since they traveled at several times the speed of sound--the noise of their arrival actually came after they had hit their targets--there was no advance warning whatsoever. The only way to defend against them was by bombing the launching sites...Fortunately for the Allies, the missiles were none too reliable so that quite a few of them never even came close to performing as planned. Gyroscopically guided, they were also extremely inaccurate. On the average, each launch only led to less than one person being killed. Indeed it is estimated that the number of slave laborers who died building them was far greater than the number of people actually killed by the missiles. The impact on Allied morale was considerable, but one can only concur with the historian who argues that, considered in terms of cost/benefit, they represented an extremely wasteful effort. (page 216-217)

Basically, the V-2 was a revolutionary weapon, and it clearly had some advantages that were utilized in future missiles. Improvements in range and accuracy were needed to make it a worthwhile weapon. Somewhat obviously, though, an unmanned rocket risks no pilot or aircrew, so the risk to German personnel was slight. The another glaring defect in the V-2 was its limited warhead, as even when it was able to hit its target it was unable to cause widespread destruction.