My suggestion is to watch Night Phoenx's postings.
He started out in 1939 buying only elite replacements and focusing only on his core forces that he would be bringing into every scenario.
And he is playing on Rommel difficulty.
In 1940 I figured out how to start posting comments on you tube, yes I am that dumb, and started giving advice.
He started applying my advice along with another poster amed Von Chocker and he is now doing such a marvelous job with his lay out and strategy that his postings will be helping me as I battle on Manstein level.
Battling on Manstein level is insane and requires buying replacements during the battle, but I limit replacements to almost always exclusively regular replacements during a battle, at least in 1939 and 1940.
Between battles it is much cheaper to buy elite replacements and free to give them regular, but if you are playing with enough artillery back up and proceed cautiously and steadily you can almost avoid any casualties, at least watching Night Phoenix's playthroughs on Rommel.
Just because it says you will hit 4 versus them hitting 0 does not mean it will happen that way, especially if they get a Rugged Defense, that is why arty and Full Suppression is very important.
At Manstein level, you cannot avoid casualties, but you can absorb losses if you build up a strong enough base of core units.
On Guderian You have to rush forward quickly to get Decisive and you have to take risks, but any other level can be proceeded with caution as on Manstein you will have to settle for a lot more Marginal Victories.
