Food was the most unsolvable issue, if trying to do a war against the British, and as expected, the Americana. It was a monthly deficit even when the Soviets were doing shipments, and they Soviets were diminishing their own reserves to make these shipments, so it was unsustainable regardless.
Oil was big, but they were while the Soviets were shipping, gaining in oil stocks every month. (Perhaps if they wanted to 10x their air force to compete with the Americans then they would need all the Baku oil)
Metals like Magnesium were big, they were getting shipments from the Soviets which covered 40-41 needs anyway.
So while they needed lot stuff from the Soviets, trade with the Soviets got a lot of things they needed in sufficient levels. And there was also transshipment, i.e. the Soviets bought rubber from the British and resold it to Germany.
Thing is is food the biggest problem and more importantly can it only be solved by the Ukraine?
By the end of 1940 Germany has occupied France and Poland (and elsewhere). don't get me wrong seizing the Ukrainian breadbasket is better but it's not the only solution they have available to them here for accessing food.
The point of the POD is if the Germans "know or guess" the Soviets can't be beaten due to the distances involved what can they do about their situation in 1941.
Thing is they already knew this an planned accordingly. It's why Barbarossa is not about getting to certain spots on the map and thus winning*. It's about quickly destroying the Red army thus ending the USSR's ability to resist and then occupying those spots on the map much more easily and reaping the resource rewards.
*which is why ATL POD's that obsess about getting some panzers into red square by having panzer div X zigging in mid Oct instead of zagging = Nazi win, miss the reality of the situation
The choices
a) Deal with the Soviets as friendly Neutrals to get the war supplies they needed (works except for food, I honestly think a non Nazi competent government could make food work, with the resources available, but that is not what the Germans had going on)
b) Invade and eventually get overextended and lose big as per OTL.
c) Do a smash and grab to get resources close at hand and go on the defensive. Rely on the fact (from the Nazi point of view of course) that the Soviets are a pathetic Commie Slav state, the even the Finns can mount a credible defense against, should be no issue for Germany.
The problem with C as presented is it ignores a few things:
1). it completely flies in the face of all German armed strategy and tactics they developed and based themselves around, which is go in quick and win quick. A strategy that had just served them very well in Poland and the west.
2). it ignores the reality of the USSR that while the German underestimated aspects of it, still knew. That the USSR once fully mobilised can basically out muscle Germany on pretty much every front. Look at the plan for Barbarossa, it's overly optimistic for several reasons but it still based on the underlying fact that Germany has to go in quick, inflict an insurmountable amount of damage and win before the USSR get's going and fully mobilises it greater population, industry and resource base.
3). If the Soviets are a pathetic commie slave race (which as you say was the German position) then you beat them and win thus solving the food problem and more besides (ties into 1 above).
4). The Winter war was the Finn's repulsing an invasion from the Soviets and a fraction of Soviet force at that. Not going into the USSR and sitting on a big chunk of soviet territory and trying to defend it. Very different situations
5). 3 assumes 2 is known, 2 was not known, and ran counter to not only Nazi ideology but the German experience of the war so far to date
6). Even 'just' taking the Ukraine and holding is still going to require a very long defensive line because they will have anchor both flanks. Plus going over to the defensive means handing the initiative to the Soviet in terms of when and where they attack which means the Germans can't concentre forces as much which is a big part of their operational playbook. (this relates back to 1).
7). lessons of WW1 (this kind of relates back to 1 and 6 but is worth picking out specifically), no one,
no one who was involved in WW1 is going to go looking for a static war based on out defending the other side along long lines of contact where all your lovely advances in mobile warfare are largely negated.
8). It still means fighting on more fronts than you need to, Germany wants to beat the USSR quick so it can go back and deal with the British/N.Africa/M.East.