I' m building a scenario on the same situation, battle of France 1940. I choose a map of 2.5 km / Hexa and each division is detailed to 7 sub unit generaly , 3 regiments, pioneer, AT unit, scout unit , artillery unit and HQ. Of course this depends of the OOB of the division and some others unit are added like, corps, wing fighter etc ...
I try to copy near as possible the historical OOB of each nation ( included regiment, battalion, ... organisation and quality) , Germany, France, UK, Belgium. I choose to don't build Holland as there are already lot of Units.
I 'm using different source to build OOB
http://www.atf40.fr/ATF40/
http://france1940.free.fr/fr_index.html
http://niehorster.orbat.com/index.htm
and Nafzinger data but the link seems to be down for nwo
So the map start from Antwer to south of Paris, and from France east border to the Ocean( Normandy included) , I use a 1946 map of France for the road and train way
so today:
the map is 99% made
All allied OOB is made
4 Germans armies are made , I' m working to finish that part
I have modified a little too the equip file as there are some false (or added some) value for 1940 equipment
So after I have to place units on map, I have good historical map for that and probably the more complicated. Teawk the game following the different possibility of the scenario editor, I 'n not an expert regarding that, help is welcome