General thoughts on what I saw and how to represent it.
Of course very little of the fighting in the Polish-Soviet war took place in modern Poland: instead taking place in the modern Ukraine and Belarus. However, the most famous battles were in Poland, which is a lot more easy to visit. The comments below only relate to the areas where the fighting took place, so not west of Warsaw or south around the Carpathian mountains.
In general the average wargames table represents the bulk of what I saw pretty well, except that any hills should be very big and gentle and any waterways wide (to represent the marshy edges). Most hills are too gentle to provide any bonuses for being uphill.
Most tables should include woods, increasingly many as one heads north.
Any low-lying area can be boggy, regardless of whether there is a water feature present. Virtually all roads will be unsealed and all rail lines unembanked.
No fields should be hedged, fenced or walled.
For the area around Radzymin, the table might as well be dead flat, with quite a few villages, some isolated farms, and lots of woods.
To represent the area north of Warsaw a wargames table can be pretty much devoid of hills but should have all waterways noted as sunk into the table: therefore units within a specified distance of them will be out of sight. Woods and villages are plentiful and there would be some scattered farms.
The area around Zamość has virtually no isolated farms but a lot of villages. It is mostly quite flat and frequently boggy. At the time of the crucial battles in the 1920 campaign there it had been very wet, and the ground was quite heavy.
The Polesie (Pripet Marshes) was not the scene of much fighting. It is mostly flat and heavily forested. Obviously it is frequently very boggy and parts of it have lots of lakes. Virtually all fighting would be along a road, since they follow the lines of substantial dry land.
These don't differ across the area enough to matter. In general villages should be plentiful and stretch in a thin strip along a road. They might have a fair number of trees, especially fruit trees around the edge.
Churches are large, but only found in the largest villages. Those same villages would be the only ones that might have a few brick buildings in the centre.
Houses can be represented by the normal wargames ones sold as "Russian", though normally they would be painted white. Tiled or thatched. Outbuildings will be natural wood.
Although uncommon now, the local nobility lived in manor houses that varied from large to huge. They would usually have a park or garden attached if of any size.
Windmills were common and I think normally on the edge of a village. The other commonly used vantage point was large haystacks.