The German war economy faced a number of constraints (i) oil (ii) steel (iii) transport chiefly rail (iv) manpower. Increasing one aspect runs afoul of other constraints. (hmm could add (v) food supply)
More divisions means rail capacity for logistics has to be increased which directly competes with rail capacity for the war economy, increasing overall rail capacity means investing steel allocations years ahead reducing production in other areas. Another example is the sharp reduction in occupied french dairy production, before the occupation the milk was picked up in trucks, but the french economy was running on about 8% of it's prewar oil, the milk simply spoiled. The Germans also took most of the french railway rollng stock as they had real shortages themselves with massively reduced oil supply, and much reduced rolling stock teh occipied french economy was a shadow of it's prewar self.
The 1941 massive Russian prisoner take was more or less deliberately starved to death (1.5 million! Though there would have been huge problems feeding them even if there was a real effort to keep them alive, the Russian POW could have been used to fix a some of the manpower shortage the overall food supply was pretty stretched. ), later Russian POW labor became valued but still much reduced productivity due to poor diet. In this 1941 the German war economy was short around 1.5 million workers, of course there is an overhead for using POWs (guards and stuff) and it's not skilled labour.
Wikipedia on Russian POWs
"Between 1941 and 1945, the Axis powers took about 5.7 million Soviet prisoners. About one million of them were released during the war, in that their status changed but they remained under German authority. A little over 500,000 either escaped or were liberated by the Red Army. Some 930,000 more were found alive in camps after the war. The remaining 3.3 million prisoners (57.5% of the total captured) died during their captivity"
Russian treatment of German POWs (wikipedia)
"According to some sources, the Soviets captured 3.5 million [ame="http://en.wikipedia.org/wiki/Axis_powers_of_World_War_II"]Axis[/ame] servicemen (excluding Japanese) of which more than a million died"
Prisoner of war - Wikipedia, the free encyclopedia
Of course with the early 1941 campaign going so well the need to prepare the German economy for a war of attrition wasnt on the Nazi minds, the war would be won soon, long term problems in the economy were not a factor in their planning such as it was.
I think Tozer's book is a good read, (though I would have preferred a more comprehensive statistical approach, he just tends to quote and example stuff that supports his narrative , of course it would have reduced it;s readability and wider appeal and made it more bulky). It's a relatively readable and breif approach to the overall German war economy. As always any particular book is never going to be the whole story. It's good, but really mainly overview stuff and no in depth analysis of the statistics.(which is want I personally am still keen to read about) It's more a start, if you want a deeper understanding you going to have to get something more detailed and analytical rather than narrative.
And when talking statistics it's not enough to just present figures, without a commentary of how they were complied (by who for what purpose under what pressures/constraints) to give (a) a feel for their accuracy (b) an understanding of any assumptions about the data the author is taking, (c) where to look for the data.
(sigh, my monolingual-ness irks me sometimes, but I not good with languages, I'm sure English isnt my native tongue but it's all I got)