..combing skilled workers out of the ranks of the Wehrmacht, to get German industry back up to its potiential. Slave labors and 'Guest Workers' were not nearly as productive as well paid German workers had been.
Which deprives the Heer of manpower which even OTL proved to be inadequate. Enemy breaks through the inadequately manned front-lines and overruns Germany. War lost, hypothetical production increase rendered irrelevant.
Slave labour allowed the Nazis to go well beyond what they would otherwise have been capable of through the ruthless expenditure of human life. This conclusion is unsettling to us, since we like to have what is evil also be what is ineffective, but the unfortunate fact is that foreign slave labour allowed significant increases in Nazi productivity at a time what the Germans simply had no other viable labour source. Their women were out farming and their men were off fighting. There was ultimately no other option. So although foreign labour was never as efficient as German workers, the Nazis literally worked them to death for nothing.
...provide auto and rail transport to prewar levels for industrial/agricultural use, without reducing that used for attacking the USSR.
Which is impossible. The Germans can either loot france for the trains and trucks to support Barbarossa or they can watch their advance collapse before it penetrates the Soviet heartland and then watch as the largely unharmed Soviet military-industrial base buries them in even more massive quantities of armaments and troops compared to OTL.
In fact what the French industry needed to retain effectiveness was coal and what the French agriculture needed was fertilizer.
Both of these are transported by rail and barges and that turned into a major bottleneck as well. You'll need to increase hydrogenation capacity for fertilizer (this is competing with ammunition), coal production for transport and for export to France and a surpluss transport capacity + orders for the French industry instead of pillaging.
It also requires sufficient stocks of coal and fertilizer to exist in the first place. As it was, German stocks of these materials were inadequate to support their own industry... so how the hell are they going to get enough to support an entire other nations industry?
It happens in my signature TL although its impact is not really understood by the readers
Largely because you just magic up the required production of coal and fertilizer, ignoring that the Germans were pushing the limits as hard as they could have OTL without derailing their war effort. Hell, if you look above, you'll note that you had inadvertently admitted that the only way the Germans could get more fertilizer is by
sacrificing ammunition production. Which, I once again am forced to reiterate,
was inadequate as it was.
The bottom line is in order to help the occupied territories industry, the Germans
have to hurt their own war effort. There would be few if any real savings if those occupiers operated more humanely and with an eye for long-term sustainability... and many economic losses compared to what the Nazis were historically able to wring out of the conquered economies. The brutality of the Nazi policies often hides the threadbare shoestring Germany waged WWII on. They had to export the hardship onto their conquests in order to keep it going as long as they could.