It would be the 100 million N. Americans against only the Germans plus the “desirable” races.
The massive extinction of these other people would not take place until everything globally were settled. I think the limited nature of the extermination would not be on the grand scale until America was dealt with. I think we are assuming a level of cooperation in former UK colonies akin with the French conquests, so the level of Serbian reaction would have been somewhat mitigated by the axis partners carving up that nation and exacting the type of ethnic violence that occurred much latter. Germany had a commitment to pit old enemies against each other in an effort to make their job easier.
The Soviets i feel would be somewhat difficult, but they did convert a few divisions of Russians who were against Stalin. The middle east was another basket of potential friends who could be enlisted easily to fight the Jews. Germany raised a number of Muslim units in the war.
If Hitler was removed, the replacement would be far worse because a NAZI victory would remove all the remaining inhibitions against violence against what they deemed lessor men. The SS would have selected somebody like Heydrich who had the most firm convictions of their type. The choice would have to be political leader, and not a military one.
On the German-Japanese partnership, i think they would not fight until USA had surrendered first. Once all opposition was gone eventually it would happen, but the Germans would have the best scientists, so the Japanese would be at a disadvantage.