Antwerp, as in real life, can be a real headache for the Germans as it
can delay them considerably. Indeed there are two approaches to deal with it which abstracts the historical reality of the dilemma. Since it is
the national redoubt of Belgium it plays a role in protecting the rest of the Belgian army as well as a potential reinforcement position of the Allies by the sea.
If you choose to storm it you need to go there with the railway guns (2nd Army) and enough ammo to play the "bombard decision". Antwerp is 2-level fort (notice the small rhombus icon), which abstracts the national redoubt perfectly. In my opinion one should NOT attempt to evict it if he hasn't first made at least 2 breaches in order to negate its defensive advantage which is considerable. On the other hand, you could choose to simply isolate it with a smaller force but this is very risky business in the long run as Antwerp can be the receiving point of a British force arriving from the sea and endanger your rear.
This is possibly one of the first and most difficult dilemmas for the Central Powers player indeed. I have tried both attempts with mixed results. If you go for it fast you might lose some steam in your Schlieffen plan, if you simply check it from the outside you risk a surprise counterattack that could disturb the logistics. In the long run I think you should evict it anyway.