Any other interesting/relevant (for this topic) points in the book? If Germany had mobilized fully before the war how come they managed to increase the output of war material after 1942?
By mid-1938, the German forces had grown much too large to sustain at peace. The German leadership essentially faced a choice between partially demobilizing or creating further provocation to justify continued growth of the military. We all know what choice was made. After 1940 Germany had a de facto empire in Europe, which it squeezed thoroughly for every kind of resource. Strategic priorities during Operation Barbarossa and 'Fall Blau' were to secure resources to continue the fight. Germany's empire essentially was trapped in an economic situation where it had to expand and take more resources or collapse. At no point after 1938 was Germany's focus elsewhere.
So you are right that Germany did continue expanding military production until it was defeated, but there was no sudden or even discernible shift in the mobilization level of the nation as a whole except a steady increase in mobilization level as the war dragged on. As the industrial weight of the British Commonwealth, the Soviet Union, and the United States continued to build against Germany, the German armaments industry became intensely focused on maximizing their immediate output in reaction to a dire strategic situation. This by itself does not indicate higher mobilization, but merely a focus on immediate production numbers. For example the Me 262, first flown in 1942, was the only air superiority fighter capable of inflicting losses upon the Allied Air Forces at a rate (5 to 1) which would've been favorable to Germany given the numerical superiority of RAF and USAAF. However due to the fact that the German economy was already incredibly mobilized by 1942, shifting production to a new resource and labor intensive model was unfeasible. The decision was made to focus late-war interceptor production on the BF 109, not a bad plane during the early war, but with a 1936 chassis that was outclassed by the P-51 and other late-war enemy fighters.
During the late war Germany produced some models which were qualitatively inferior to previous models (Panzer IV Ausf. J). Shifting to a more advanced model (Me 262, Panther, MP44/Gewehr 43) would've interrupted supply at a critical time so older, increasingly inadequate, models (BF 109, Pz4, Karabiner 98k) continued to be produced in greater numbers. A lot of the late war increase in numbers can be attributed to experience gained producing the same model. Production numbers alone do not tell the complete story in regard to mobilization of Germany.
Was this done at the expense of some other industrial products?
The entire rearmament process which Germany undertook was largely at the expense of it's civilian sector. Shortly after the Nazi party took power, the living standard for Germans recovered to 1929 levels (also not very high compared to the Western Democracies) but didn't increase much after 1935. Pre-War prices for civilian items in Germany were relatively much higher than in France, UK and USA. For example much hoopla is made about the
Volksempfänger program, which was the government's plan to make civilian radios affordable to the German general public. It is interesting to note at the height of the
Volksempfänger program, consumers in the United States had access to higher-quality radios that were also less-expensive.
Also one common criticism of Nazi war production is that they failed to implement true mass production and instead opted for more labour intensive production. If they hit the cap of raw materials before that was this really a problem? Is this just a case of over fixation on tank and submarine production?
The fact that German manufacturing was less efficient than the USA and Britain doesn't have much to do with relative mobilization, and more to do with relative industrialization. Germany didn't "opt" to have a smaller industrial base, certainly if they had a choice they would opt out of this.
So as soon as the United States entered the war, it could convert it's massive automobile factories to war production. Germany had the beginnings of an automobile industry in 1939, but in order to achieve the numbers it did late-war it had to first build the factories and also train the metalworkers to work in them. The German leadership wanted to emulate the United States in this regard, "Fordist" was literally a buzzword for Germany while it was rearming, but it could not realize the kind of efficiency the United States was able to achieve simply due to economies of scale. For Germany it proved almost impossible to create a modern efficient automotive industry in less than a decade from virtually nothing and a consumer base which largely couldn't afford to buy it's automobiles. But because Germany was mobilizing in the 1930s, it tried
really really hard.
Today it is ingrained in our collective consciousness that Germany is a rich country with a highly advanced industrial base (with especially swanky automobiles), but this was not the Germany at the time of HoI. In the Germany of the 1930s, on one hand you had internationally competitive companies with very advanced laboratories (IG Farben) and sophisticated machinery (Siemens and BMW) but then on the other hand, you had the majority of Germany's population working on small subsistence farms with a median living standard similar to that of it's central European neighbors. Our modern conception of what the German economy is capable of came about through the
Wirtschaftswunder in West Germany of the 50s and 60s, but back in the 30s Germany was very much one nation with two very different economies.
And finally, Germany faced an acute manpower shortage through the entire war. Labour might not have been as intense a resource bottleneck as fuel or tungsten, but it definitely was a huge issue. One example I am actually allowed to cite would be that in July 1944 the Ministry of Armaments mandated a 72 hour work week for workers in tank factories. A craftman in a factory = one less soldier. Raw materials, no matter what they are, also require manpower to obtain. A miner in a coalmine also = one less soldier.