Actually rommel was in effective control of 17 divs but more importantly, more than 30000 trucks....more than the entire allocation to Army group north. 5 of the 17 divs were german , and nearly the entire mobile formations of the italian army. Technically the italians were under their own command structure, but in reality those in North Africa were under the command of DAK, who could also reasonably be extrapolated to include various overseas italian forces in this scenario. These arrangements placed at Rommels disposal 21st Panzer, 15 Panzer, Ariete, Littorio, later Centauro Armoured Divs, Gruppo Malletti (a poorly formed and organized armoured group that was in the process of reorganizing in 1940), Trieste and Trento Mot Divs (one lost its trucks historically), 164 Light, 10th Bersagliri Motorized formations. His Infantry included Ramcke brigade, Folgore airborne, 7th airborne, a mountain Div (in Crete), 27th 61st, 62, "Pavia", 136th Gio Fascisti Divs 3-4 divisions in Sicily (for the invaskion of Malta)Armoured Divs, 4 divs destroyed in O'Connors offensive, a further 5 divs in Abysynnia that were destroyed, including the Duca Aosta Grenadiers, an elite Italian group that fought with distinction at Keren. In Greece the Italians had committed 10 divs eventually. There were hordes of light tank battalions in both NA and Greece.
This is by no means a complete list, just a taste of the forces committed to the southern front in 1941-2, and which reasonably can be allocated or expected by Rommel. It amounts to nothing, however, because the starting premise is broken. Germany was allied with the Soviets in 1939, and this allowed the Germans a free hand in Poland and vital economic assistance in 1939-41. without that the Germans are unlikely to attack in Poland. If Poland is not attacked, Germany does not go to war againt the West. The romanians remain allied to France, Hungary remains aligned to Italy. Germany is starved of half her oil. If the Germans attack any of these eastern european nations it can be expected the west will give gurantees to them like they did for Poland, and we are back where we started...except that Germany loses most of what friends she has, because most of these nations have trade arrangements with the Germans and economically is in big trouble because she loses about 80% of her foreign trade.
It is an unrealistic scenario to surmise a war between Germany and Russia without a war with the west. One scenario is that Germany attacks Poland without a non aggression pact. Almost certainly Poland will be overrun, but there is no trading relationship with Russia and the british blockade of germany turns her economy south almost immediately..Germany did not have the economic depth that she had in 1914....and this means the blockade has nasty and immediate potential except if continental trade is maintained....the war would be over by the end of 1940. Once at war, the British and french made their terms very clear, and capitulation just want on the cards. there were several attempts made at mediation after Poland, they all got nowhere .
So, if we are assuming a DoW between Russia and Germany 1939 to 1941, with the wst not involved, it has to be early....1939, at the latest, and it will have to go around Poland, and have no friends like Finland Romania and Hungary. There is no injection of resources as occurred after the fall of France, and the low countries. If we assume that France is attacked and overrun, then we are back againwith a hostile Britain fighting as she did....no change to the scenario. There are no conceivable scenarios that create a mechanism for an early British capitlation. we can wave the magic wand and say "oh the scenario demands it" Okay, but it was never going to happen.
So we are back at this point in 1939, where Germany attacks the Soviets 1n 1939. Cant go through the Baltic States, they are still independant, if attacked by Germany, they will alienate a still living Poland, Finland etc and risk involvement by the west. Leaves the area on the southern side of the Gulf Of Finland next to Leningrad. no ports of any significance, constricted waterways, Germans have a lift capability not exceeding 2 divs, amphibs into enemy controlled waters, mine infested, and reserves of 40 divs in 1939. Cant be done.....
I repeat, it is simply inconceivable that Germany could go to war with the Soviets alone. In any event, there would be quid pro quos if it was attempted, and none of them favour the germans. germany hoistorically attacked the Russians under the most favourable conditions that she could organise, and still could not defeat the Soviets. They simpoly did not have the resources to do so. Bernard Montgomery once said....only a fool would attempt to conquer Russia from western Europe. he knew what he was talking about