The real answer to this is simple.
Do not try to reenvent the wheel in any way, use all our standard object layouts. Changing basic game play stuff can have lots of unforseen consiquences.
Don't put any thing in the terrain just because you think it's cool. i.e. stuff like bridges new river types and such.
Keep fields spaced corrently i.e. between 3/4 and 1.5 sectors is min max, normal try keep field spacing to 1 sector.
Never sacrifice game play over real land mass or real field layouts.
Rember players will abuse any diffencancy in the terrain.
Vehicle spawn point to base is normal around 5miles from the tower.
Finaly:
Rember you are not creating a terrain for yourself or to show people how inovative your are,or because you found one wwii era facinating, you are making terrains for other people to have fun at.
And if you realy wish to make a main arena terrain, save yourself lots of work , make a simple bitmap of land mass and field/factor/city/hq layout, send it to us befor you start the real work.
Good luck.