As for what I think you should have done, Ezio, it's though to say. I can definitely see why you did what you did. Russia was a threat that needed to be dealt with.
However, by abandoning Belgium, you pretty much gave it to France. It's no-press. You were pretty much just expecting him to leave it alone, out of the goodness of his heart. He he had 4 units on that front. He wouldn't just leave them sitting around while there are free centres to be taken.
Had I been in your position, I would have held Bel and Ruhr, while moving Mun-Sil. You knew you had a build coming, so that could have easily reinforced you against Russia without moving everything else as well.
I would have hope that France move into the Med and leaves you alone. By keeping units on his front, you give him less incentive to attack you.
Though this is a different season, I really don't thing moving NwgS-Edi in S04 was the right move, and I think it contributed to your problems in A04. Edi didn't need covering, since no one could attack it. Edi is also a really useless province to keep fleets in. If it wasn't a SC, I'd say it's almost as bad as Clyde.
Anyways, by sticking the fleet in Edi, you had less options around the North Sea in the Fall. In the alternate universes where you didn't move to Edi, you could have been a turn ahead in taking the North Sea, by not bouncing with Russia in A04. Who knows where your chances could have gone from there.