What if Operation Barbarossa was cancelled in 1941, and instead, Germany invaded, partitioned or conquered the remaining neutral countries in mainland Europe?
- Portugal
- Turkey
- Switzerland
How long would the Soviets play along?
If the Soviets partitioned Turkey with Germany, would the Western Allies be more suspicious of Soviet Union later on?
"Sweden had long been Germany's main source of high quality iron ore and
ball bearings"
Spain was in a disastrous economic situation (was on a verge of starvation) and not hostile to Germany (IIRC, it even provided division of volunteers) so its occupation would not make too much of a practical sense except for a possibility of capturing Gibraltar but even this goal would require a big logistic effort. In OTL "Spanish companies did important aircraft work for the Germans, Spanish merchants furnished Germany with industrial diamonds and platinum, and war materials, among them mercury and tungsten. Spain, the world's second-largest producer of tungsten after Portugal, provided Germany with 1,100 metric tons of the ore per year between 1941 and 1943 (between them Spain and Portugal provided 90% of Germany's annual 3500 tons requirement)". IIRC, the US managed (or at least tried) to exercise some influence by food supply program.
"Portugal provided Germany with direct overland exports of a wide range of commodities including rice, sugar, tobacco, wheat,
potassium chlorate, inflammable liquids and
yellow pitch, and Portuguese merchants were also known to be sending industrial diamonds and
platinumvia Africa and South America. But by far the most important material Portugal had to offer was tungsten. Portugal was Europe's leading supplier of tungsten (and
scheelite, another member of the
wolframite series of tungsten ore minerals), annually providing Germany with at least 2,000 metric tons between 1941 and mid-1944, about 60 percent of her total requirement."
"Turkey, who in October 1941 began selling Germany large quantities of
chromite ore for the production of chromium. The Turkish chromite ore, which like tungsten was an irreplaceable and essential war material, was the only supply available to Germany".
"Switzerland was of no strategic importance to Germany, and of far more use to her as a workshop....
Oerlikon-Bührle provided guns, Autophon A.G. provided transmitting apparatus, and other companies exported coal-gas generators, ball bearings, bomb sights, ammunition, carbon black, timepieces and
rayon for parachutes.... she remained able to move imports and other exports such as sugar and
benzene overland, mainly to Germany and other countries in the neutral zone.... Swiss were, and continue to be, criticised for the way they aided the shipment of Nazi funds abroad and provided banking facilities for the concealment of looted art treasures and gold, much of it stolen from Jews."
https://en.wikipedia.org/wiki/Blockade_of_Germany_(1939-1945)
In other words, what would be a practical sense in occupation (which would take a considerable effort to accomplish and maintain) if there was a cooperation (does not matter, volunteer or not)?
BTW, would not occupation of Spain and Portugal more or less imply the end of Vichy France just to simplify military operations? Or do you consider a joined German-Vichy campaign?
But if we assume your scenario, then, with a possible exception of Turkey, the SU, as long as MR Pact holds, would be mostly irrelevant even simply because it did not have common borders with the rest of the countries on your list. Predicting short- and long-term Stalin's attitudes is a waste of time but it is probably reasonable to assume that Soviet military reform would keep going on and the same applies to their military industry. Possibility of an aggressive action would be probably based on the balance of the following:
(a) Further German military successes - a deterrent.
(b) Growing German industrial/material base - a deterrent.
(c) If occupation of the new territories involves considerable permanent German presence all over the map at the expense of their "mobile" force and if there are noticeable problems with keeping all these territories under control, then there may be a temptation, especially if by that time a meaningful participation of the British and US forces became a reality (and there is a possibility of a big-scale US/UK help along the OTL LL lines).
As for the US/UK being suspicious, why would Turkey cause more awareness than Poland, Latvia, Lithuania, and Estonia? Of course, Soviet annexation of some Turkish territory would move their border closer to the British-controlled Middle East but after Hitler's attack, the Brits were OK about the joined occupation of Iran. Also, I don't think that WC had any illusions about Stalin while FDR was seemingly looking at the situation from a perspective of defeating Germany ASAP and then leaving the European issues to the Europeans making US presence there as short as possible. Why would he bother about post-WWII Turkey more than about post-WWII Eastern Europe?