No, thank you for the input, otherwise I would have learned the hard way, that my setup will not work.
Only Germany will get the TN tech at game start, but the other nations will try to research it.
Using SM like you mentioned might still make it viable. With the UK being most likely the first target for Germany due to its fairly high research (with 4 labs and 5k for TN tech it should take about 5 years to complete the research). Essentially the same time it will take Germany to research Mobile Infantry.
After this war it will be about 50 German divisions (most likely still largely low tech INF with some low tech ARM and a couple of Mobile INF minus whatever is still needed to control 350m+ pops from the UK by this time) vs. 100 divisions (all low tech INF) from the rest of the world when the second war starts. And the longer Germany waits to build up the more nations will get to TN and research either GAR or improved combat values. In addition each other "major" has a Training Facility and Germany either just 1 or maybe 2 if the UK one does not get destroyed (2:7 at best).
Without the UK's industry the rest of the world has about 1.4k conventional factories with Germany having about 120 converted ones and 760 from the UK (at occupied production).
Essentially Germany has a 5-6 year headstart and especially due to the difference in starting divisions and TF I am not sure if Germany will win. My fall-back option is that the rest of the world stays united after defeating Germany and head for the stars
All of Earth has 27 labs at game start (minus whatever gets destroyed in the wars), so once Earth is unified research speed should actually be decent and pop numbers most likely around 1.5bn. But as an additional handicap I will limit resources on Earth with none on Luna.
The basic idea is to give NPRs a fairly long time to expand and build up while there is still stuff happening on Earth.